我看著python書上的linebot製作教學時在執行程式的時候發現一直出現405錯誤，請問我該怎麼處理或怎麼修改，我查了一下網路好像是憑證出了問題(?我也不太確定

from flask import Flask
app = Flask(__name__)

from flask import request ,abort
from linebot import LineBotApi,WebhookHandler
from linebot.exceptions import InvalidSignatureError
from linebot.models import MessageEvent,TextMessage, TextSendMessage

line_bot_api = LineBotApi('Channel access token')
handler = WebhookHandler('Channel secret')

@app.route("/callback",methods=['POST'])
def callback():
    signature = request.headers['X-Line-Signature']
    body = request.get_data(as_text=True)
    try:
        handler.handle(body,signature)
    except InvalidSignatureError:
        abort(400)
    return 'OK'

@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    line_bot_api.reply_message(event.reply_token,TextSendMessage(text=event.message.text))


if __name__=='__main__':
   app.run()