The Web hook should accept request with POST method? Secondly, When I tried to POST a payload, it showed method not allowed error

Webhook is created in Flask and hosted on the google cloud Platform. Link to the web hook URL. https://webhook-app-305615.df.r.appspot.com/

Please explain how to develop the post method.

from flask import Flask, jsonify, request
    
app = Flask(__name__)
@app.route('/')
@app.route('/api/echo-json', methods=[ 'POST'])                                                                                                    
def add():                                                                                                                              
    data = request.get_json()
    return jsonify(status=200,info='OK')

When you get the payload in webhook, it should always return a 200 ok HTTP JSON response. Sample Payload to be received:

   {
    "uri" : "https://webhook-app-305615.df.r.appspot.com/",
    "data" : {
        "messagepreview" : "Hi",
        "connectionname" : "919995669111",
        "uri" : "whatsappsandbox://919995669111@2935e36-983a1b8",
        "receiveraddress" : "919995669111",
        "senderaddress" : "6585909227",
        "attachment" : {
            "value" : "Hi"
        },
        "timestamp" : 1563183428,
        "attachmenttype" : "text",
        "webhookaccesskey" : "abc-xyz",
        "parts" : [{
                "contentType" : "text",
                "data" : "Hi",
                "uri" : "",
                "originalEvent" : "{\"from\":\"919995669111\",\"id\":\"ABEGkMT-o1QcQQ4GP\",\"text\":{\"body\":\"Hi\"},\"timestamp\":\"1563183428\",\"type\":\"text\",\"profile\":{\"name\":\"John\"}}"
            }
        ],
        "sender" : "whatsappsandbox://6585909227",
        "receiver" : "whatsappsandbox://919995669111@whatsapp.com?name=John"
    }
}