How To Create a LINE ChatBot

Create an Account
Create a Channel
Webhook - A Simple "Echo"
Reply an Image File (JPG, PNG or GIF)
Reply a Picture + a Message
Get the User ID
Actively Push Messages to Users
Broadcast a Text Message
Broadcast a Flex Message
Handle an Uploaded Image File
Recognize an Uploaded Image File with PIL
Handling Other Types of Files
Flex Messages
Flex Hierarchy
Carousel
Button
Postback

Create an Account

Go to LINE Business ID and click "LINE account". (I assume that each of you already has an LINE account.)

If this is the first that you create a LINE ChatBot, you will be required to create a Business ID.

You will then be required to create an "Official Account".

This step will authenticate you via SMS (Short Message Service, 簡訊).
Actually, you may create more than one "Official Account" - one account for each ChatBot channel.
You obtain a "Bot Basic ID" (e.g., "@160qyrjz").
Click "Verify Later" and go to "LINE Official Account Manager" (in my case, it will be "https://manager.line.biz/account/@160qyrjz/").
You don't need to start gathering friends at this moment, so you may simply close the following pop-up window and go to the home screen of "LINE Official Account Manager".
Now the official account is automatically added as your LINE friend. However, if you sent it any message, it would be unable to respond yet, because you haven't written programs to tell it how to respond.
- 感謝您的訊息！
  很抱歉，本帳號無法個別回覆用戶的訊息。
  敬請期待我們下次發送的內容喔

Create a Channel

Click "Settings" at the top-right corner, then click "Messaging API" at the left pane. Enable Messaging API.
Select a Provider.
- If you create "New Provider"
  You may input an arbitrary "Provider Name". This has nothing to do with your chatbot. You may simply use your nickname (e.g., "Mendelssohn"), and press "Create".
- In my case, I re-use "Solomon" rather than creating a new provider.
If you haven't decided your privacy policy yet, simply press "OK" to skip it. You may edit it later by visiting LINE Developer Console and modify the "Basic Settings" of the channel.
It wants you to confirm that you want to be linked to the provider. Press OK.
Now you have successfully created a LINE channel. You don't need to write down the "Channel Secret". You can always find it in "LINE Developers Console" later.

Webhook - A Simple "Echo"

As shown in the figure of https://developers.line.biz/en/docs/messaging-api/getting-started/, you have to run a Flask program, which receives a message from the LINE Platform, and replies accordingly. For security reason, the message must be transmitted by HTTPS.
Use SSH to connect to "kghs2.ncnu.net". Login as "s114xxx".
Go to LINE Developers Console. Select your channel.
- Under "Basic settings", find "Channel secret". Store it in an environment variable. (e.g., "export CHANNEL_SECRET=xxx")
- Under "Messaging API", obtain "Channel access token". Store it in an environment variable. (e.g., "export CHANNEL_ACCESS_TOKEN=yyy") If there is no token yet, click the "Issue" button.

Create a Python program "chatbot.py":

from flask import Flask, request, abort
import os

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, TextSendMessage,
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)


@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']

    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)

    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)

    return 'OK'


@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    msg = 'You said: ' + msg.upper()
    line_bot_api.reply_message(
        event.reply_token,
        TextSendMessage(text=msg))

Run "flasks --app chatbot.py run". Note that this will run your Flask over HTTPS.
Go to "Messaging API" and edit your Webhook URL to be "https://kghs2.ncnu.net:140xx/callback". (Don't forget the "/callback".) Click "Verify". You should see "Success - OK".
- If you got an error code "400 Bad Request", please double-check that you supplied the correct Channel Secret. Some students may mistakenly copy the LINE user ID (which starts with "U44").
Enable "Use webhook".
Among the items below "Use webhook", there is an item "Auto-reply messages". Click its "Edit". Disable "Auto-response messages". (This is the one which replies "感謝您的訊息！很抱歉，本帳號無法個別回覆用戶的訊息。敬請期待我們下次發送的內容喔.")
Now go to your LINE App and send a message "Good afternoon" to this channel (NCNU_ACM). You will see the response.

If you want to change your account name and icon, go to LINE Official Account Manager and "Edit Profile".

Reply an Image File (JPG, PNG or GIF)


from flask import Flask, request, abort
import os

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, TextSendMessage, ImageSendMessage,
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)


@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']

    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)

    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)

    return 'OK'

PREVIEW_URL = 'https://ipv6.ncnu.org/Images/ncnu_logo-100x100.png'
IMAGE_URL = 'https://ipv6.ncnu.org/Images/ncnu_logo-500x500.jpg'

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    image_message = ImageSendMessage(
        original_content_url = IMAGE_URL,
        preview_image_url=PREVIEW_URL)
    line_bot_api.reply_message(
        event.reply_token,
        image_message)

Reply a Picture + a Message

The reply_token is valid for replying only one message. If you want to reply a text message and a picture, you may reply a list of messages:

line_bot_api.reply_message(
        event.reply_token,
        [TextSendMessage(text="NCNU"), image_message])

Get the User ID


from flask import Flask, request, abort
import os

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, TextSendMessage,
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)


@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']

    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)

    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)

    return 'OK'


@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    msg = 'Version 1.4\nYou said: ' + msg.upper()
    user_id = event.source.user_id
    profile = line_bot_api.get_profile(user_id)
    display_name = profile.display_name
    msg += f'\nuser_id: {user_id}\ndisplay_name: {display_name}'
    msg += f'\nlanguage={profile.language}\npicture_url={profile.picture_url}'
    msg += f'\nstatus_message={profile.status_message}\nuser_id={profile.user_id}'
    line_bot_api.reply_message(
        event.reply_token,
        TextSendMessage(text=msg))

Actively Push Messages to Users

from flask import Flask, request, abort
import os

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, TextSendMessage, ImageSendMessage,
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)

@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']

    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)

    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)

    return 'OK'


PREVIEW_URL = 'https://ipv6.ncnu.org/Images/ncnu_logo-100x100.png'
IMAGE_URL = 'https://ipv6.ncnu.org/Images/ncnu_logo-500x500.jpg'
USERS = []

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    if msg.lower().strip() == '/subscribe':
        USERS.append(event.source.user_id)
        line_bot_api.reply_message(
            event.reply_token,
            TextSendMessage(text='Successful Subscription'))

@app.route('/push')
def push():
    for user in USERS:
        notify(user)
    return f'Messages pushed to {len(USERS)} users.'

def notify(user_id):
image_message = ImageSendMessage(
        original_content_url = IMAGE_URL,
        preview_image_url=PREVIEW_URL)
    text_message = TextSendMessage(
        text='Do you want to order lunch? 學餐三樓特價中!')
    line_bot_api.push_message(
        to=user_id,
        messages=[text_message, image_message])

Broadcast a Text Message to Users in a Channel

def broadcast_text():
    # 1. Configuration
    # Replace 'YOUR_CHANNEL_ACCESS_TOKEN' with your actual token
    ACCESS_TOKEN = os.getenv('CHANNEL_ACCESS_TOKEN')
    URL = 'https://api.line.me/v2/bot/message/broadcast'

    headers = {
        'Content-Type': 'application/json',
        'Authorization': f'Bearer {ACCESS_TOKEN}'
    }
    # 2. Message Payload
    # You can send up to 5 messages in a single broadcast
    data = {
        "messages": [
            {
                "type": "text",
                "text": "Hello! This is a broadcast message from NCNU_CSIE_Solomon 🚀"
            }
        ]
    }
    # 3. Execution
    response = requests.post(URL, headers=headers, data=json.dumps(data))
    # 4. Result Handling
    if response.status_code == 200:
        print("Broadcast sent successfully!")
    else:
        print(f"Error: {response.status_code}")
        print(response.text)

Broadcast a Flex Message

def broadcast_flex():
    # 1. Configuration
    # Replace 'YOUR_CHANNEL_ACCESS_TOKEN' with your actual token
    ACCESS_TOKEN = os.getenv('CHANNEL_ACCESS_TOKEN')
    URL = 'https://api.line.me/v2/bot/message/broadcast'
    headers = {
        'Content-Type': 'application/json',
        'Authorization': f'Bearer {ACCESS_TOKEN}'
    }
    # 2. Message Payload
    flex_json_string = r'''{
      "type": "bubble",
      "footer": {
        "type": "box",
        "layout": "vertical",
        "contents": [
          {
            "type": "button",
            "style": "primary",
            "action": {
              "type": "uri",
              "label": "CNN",
              "uri": "https://cnn.com/"
            }
          },
          {
            "type": "button",
            "style": "secondary",
            "action": {
              "type": "message",
              "label": "OK",
              "text": "ok"
            }
          }
        ]
      }
    }'''
    data = json.loads(flex_json_string)
    # 3. Execution
    response = requests.post(URL, headers=headers, data=json.dumps(data))
    # 4. Result Handling
    if response.status_code == 200:
        print("Broadcast sent successfully!")
    else:
        print(f"Error: {response.status_code}")
        print(response.text)

Handle an Uploaded Image File
from flask import Flask, request, abort
import os

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, ImageMessage,
    TextSendMessage, ImageSendMessage, 
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)

@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']
    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)
    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)
    return 'OK'


@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    line_bot_api.reply_message(
            event.reply_token,
            TextSendMessage(text='Please upload a picture.'))

STATIC_DIR = 'static/user_uploads'
os.makedirs(STATIC_DIR, exist_ok=True)

@handler.add(MessageEvent, message=ImageMessage)
def handle_image_message(event):
    message_id = event.message.id
    # print(f'User uploads a file with id={message_id}')
    message_content = line_bot_api.get_message_content(message_id)
    file_path = os.path.join(STATIC_DIR, f'{message_id}.jpg')
    with open(file_path, 'wb') as f:
        # Iterate over the content in chunks and write to the file
        for chunk in message_content.iter_content():
            f.write(chunk)
    print(f"File successfully saved at: {file_path}")

Recognize an Uploaded Image File with PIL
from flask import Flask, request, abort
from PIL import Image
import io
import os

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, ImageMessage,
    TextSendMessage, ImageSendMessage, 
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)

@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']
    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)
    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)
    return 'OK'

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    line_bot_api.reply_message(
            event.reply_token,
            TextSendMessage(text='Please upload a picture.'))

@handler.add(MessageEvent, message=ImageMessage)
def handle_image_message(event):
    message_id = event.message.id
    message_content = line_bot_api.get_message_content(message_id)
    image_bytes = io.BytesIO(message_content.content)
    with Image.open(image_bytes) as img:
        width, height = img.size  # img.size returns a tuple (width, height)
        format = img.format       # e.g., 'JPEG' or 'PNG'
    msg = f'Received file - Dimension: {width}x{height}, Format: {format}'
    line_bot_api.reply_message(
        event.reply_token,
        TextSendMessage(text=msg)
    )


Handling Other Types of Files

In addition to ImageMessage, the LINE platform also recognizes
AudioMessage (.m4a, .mp3) and VideoMessage (.mp4) types.  Please make sure to use correct file extensions.
When a user uploads a file that is not a recognized media type (image, video, audio, or a sticker), such as a .cpp, .txt, .pdf, or .zip file, the LINE Messaging API handles it using the generic FileMessage type.
The event object contains specific properties that allow you to identify and retrieve the file:
    
    id (The value is a string like '594382346082582836'.)
    
type (The value is always a string 'file'.)
    
file_name (The original name of the uploaded file.)
    
file_size (in bytes)
    
For image messages, the type is 'image', and it does not have properties 'file_name' or 'file_size'.

from flask import Flask, request, abort
import os

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, FileMessage,
    TextSendMessage,
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)

@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']
    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)
    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)
    return 'OK'

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    line_bot_api.reply_message(
            event.reply_token,
            TextSendMessage(text='Please upload a file.'))

STATIC_DIR = 'static/user_uploads'
os.makedirs(STATIC_DIR, exist_ok=True)

@handler.add(MessageEvent, message=FileMessage)
def handle_uploaded_file(event):
    message_id = event.message.id
    file_name = event.message.file_name # e.g., 'main.cpp'
    file_size = event.message.file_size
    message_content = line_bot_api.get_message_content(message_id)
    file_path = os.path.join(STATIC_DIR, f'{file_name}')
    with open(file_path, 'wb') as f:
        # Iterate over the content in chunks and write to the file
        for chunk in message_content.iter_content():
            f.write(chunk)
    print(f"File successfully saved at: {file_path} ({file_size} bytes)")


Flex Messages

Flex Messages are messages that offer an extensive and interactive layout compared to ordinary LINE messages. Ordinary LINE messages deliver only a single source type, such as text, image, and video.
Flex Messages have a hierarchical structure for building blocks, in three levels. The top level is container, followed by blocks (header, hero, body, footer) and then components. 


Components in a Flex Message is defined in JSON.
The following is a simple example for "Hello World".
from flask import Flask, request, abort
import os
import json

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, ImageMessage,
    TextSendMessage, ImageSendMessage, FlexSendMessage,
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)

@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']
    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)
    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)
    return 'OK'

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    flex_json_string = r'''{
      "type": "bubble",
      "body": {
        "type": "box",
        "layout": "horizontal",
        "contents": [
          {
            "type": "text",
            "text": "Hello,"
          },
          {
            "type": "text",
            "text": "World!"
          }
        ]
      }
    }'''
    flex_msg = FlexSendMessage(
        alt_text='Flex Message',
        contents=json.loads(flex_json_string))
    line_bot_api.reply_message(
            event.reply_token,
            flex_msg)



Flex Hierarchy
from flask import Flask, request, abort
import os
import json

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, ImageMessage,
    TextSendMessage, ImageSendMessage, FlexSendMessage,
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)

@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']
    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)
    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)
    return 'OK'

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    flex_json_string = r'''{
      "type": "bubble",
      "header": {
          "type": "box",
          "layout": "vertical",
          "contents": [
            {
              "type": "text",
              "text": "ORDER CONFIRMED"
            }
          ],
          "backgroundColor": "#27ae60"
      },
      "hero": {
        "type": "image",
        "url": "https://ipv6.ncnu.org/Images/ncnu_logo-100x100.png",
        "size": "full",
        "aspectRatio": "2:1"
      },
      "body": {
        "type": "box",
        "layout": "horizontal",
        "contents": [
          {
            "type": "text",
            "text": "Hello."
          },
          {
            "type": "text",
            "text": "Thanks for your purchase.",
            "wrap": true
          }
        ]
      },
      "footer": {
      "type": "box",
        "layout": "horizontal",
        "contents": [
          {
            "type": "button",
            "style": "primary",
            "action": {
              "type": "message",
              "label": "YES",
              "text": "Yes"
            }
          },
          {
            "type": "button",
            "style": "secondary",
            "action": {
              "type": "message",
              "label": "NO",
              "text": "No"
            }
          },
          {
            "type": "button",
            "style": "link",
            "action": {
              "type": "uri",
              "label": "CNN",
              "uri": "https://cnn.com/"
            }
          }
        ]
      }
    }'''
    flex_msg = FlexSendMessage(
        alt_text='Flex Message',
        contents=json.loads(flex_json_string))
    line_bot_api.reply_message(
            event.reply_token,
            flex_msg)

Carousel



from flask import Flask, request, abort
import os
import json

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, TextSendMessage, ImageSendMessage,
    FlexSendMessage,
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)


@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']

    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)

    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)

    return 'OK'

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    flex_json_string = r'''{
      "type": "carousel",
      "contents": [
        {
          "type": "bubble",
          "body": {
            "type": "box",
            "layout": "horizontal",
            "contents": [
              {
                "type": "text",
                "text": "Alice",
                "color": "#ff0000"
              }
            ]
          }
        },
        {
          "type": "bubble",
          "body": {
            "type": "box",
            "layout": "horizontal",
            "contents": [
              {
                "type": "text",
                "text": "Bob",
                "color": "#00ff00"
              }
            ]
          }
        },
        {
          "type": "bubble",
          "body": {
            "type": "box",
            "layout": "horizontal",
            "contents": [
              {
                "type": "text",
                "text": "Carol",
                "color": "#0000ff"
              }
            ]
          }
        },
        {
          "type": "bubble",
          "body": {
            "type": "box",
            "layout": "horizontal",
            "contents": [
              {
                "type": "text",
                "text": "Daniel",
                "color": "#00ff00"
              }
            ]
          }
        }
      ]
}
    '''
    flex_message = FlexSendMessage(
        alt_text="Charlie's Angels",
        contents=json.loads(flex_json_string))
    line_bot_api.reply_message(
        event.reply_token,
        flex_message)



Button
More actions can be found 
here.
I think the most useful ones are
    
    Postback
    Message
    
URI
    
from flask import Flask, request, abort
import os
import json

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, ImageMessage,
    TextSendMessage, ImageSendMessage, FlexSendMessage,
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)

@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']
    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)
    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)
    return 'OK'

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    flex_json_string = r'''{
      "type": "bubble",
      "header": {
          "type": "box",
          "layout": "vertical",
          "contents": [
            {
              "type": "text",
              "text": "ORDER CONFIRMED"
            }
          ],
          "backgroundColor": "#27ae60"
      },
      "hero": {
        "type": "image",
        "url": "https://ipv6.ncnu.org/Images/ncnu_logo-100x100.png",
        "size": "full",
        "aspectRatio": "2:1"
      },
      "body": {
        "type": "box",
        "layout": "horizontal",
        "contents": [
          {
            "type": "text",
            "text": "Hello."
          },
          {
            "type": "text",
            "text": "Thanks for your purchase.",
            "wrap": true
          }
        ]
      },
      "footer": {
        "type": "box",
        "layout": "horizontal",
        "contents": [
          {
            "type": "button",
            "style": "primary",
            "action": {
              "type": "message",
              "label": "YES",
              "text": "Yes"
            }
          },
          {
            "type": "button",
            "style": "secondary",
            "action": {
              "type": "message",
              "label": "NO",
              "text": "No"
            }
          },
          {
            "type": "button",
            "style": "link",
            "action": {
              "type": "uri",
              "label": "CNN",
              "uri": "https://cnn.com/"
            }
          }
        ]
      }
    }'''
    flex_msg = FlexSendMessage(
        alt_text='Flex Message',
        contents=json.loads(flex_json_string))
    line_bot_api.reply_message(
            event.reply_token,
            flex_msg)

Postback
from flask import Flask, request, abort
import os
import json

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, PostbackEvent, TextMessage, ImageMessage,
    TextSendMessage, ImageSendMessage, FlexSendMessage,
)

app = Flask(__name__)

# Channel access token
CHANNEL_ACCESS_TOKEN=os.getenv('CHANNEL_ACCESS_TOKEN')
line_bot_api = LineBotApi(CHANNEL_ACCESS_TOKEN)
# Channel Secret
CHANNEL_SECRET = os.getenv('CHANNEL_SECRET')
handler = WebhookHandler(CHANNEL_SECRET)

@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']
    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)
    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)
    return 'OK'

@handler.add(PostbackEvent)
def handle_postback(event):
    ''' Postback allows you to send data to your Flask program
        without starting a web browser. '''
    postback_data = event.postback.data  # ← Here: "sid=123&answer=yes"
    # Parse the data (e.g., as query parameters)
    import urllib.parse
    params = urllib.parse.parse_qs(postback_data)
    sid = params.get('sid', [''])[0]
    answer = params.get('answer', [''])[0] 
    print(sid, answer)
    #reply_text = f"Received postback: {postback_data}"
    #print(reply_text)
    #line_bot_api.reply_message(
    #    event.reply_token,
    #    TextSendMessage(text=reply_text)
    #)

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    msg = event.message.text
    flex_json_string = r'''{
      "type": "bubble", 
      "footer": {
        "type": "box",
        "layout": "vertical",
        "contents": [
          {
            "type": "button",
            "style": "primary",
            "action": {
              "type": "postback",
              "label": "YES",
              "data": "sid=123&answer=yes",
              "displayText": "Yes"
            }
          },
          {
            "type": "button",
            "style": "secondary",
            "action": {
              "type": "postback",
              "label": "NO",
              "data": "sid=123&answer=no",
              "displayText": "No"
            }
          }
        ]
      }
    }'''
    flex_msg = FlexSendMessage(
        alt_text='Flex Message',
        contents=json.loads(flex_json_string))
    line_bot_api.reply_message(
            event.reply_token,
            flex_msg)