While creating smartApp ,it response with error code 422

SmartThing Api: https://api.smartthings.com/v1/apps
“appName”: “Testingapp”,
“displayName”: “Abc”,
“description”: “Abc”,
“singleInstance”: false,
“webhookSmartApp”: {
“targetUrl” : “https://17ecbf03.ngrok.io/v1/appresponse

Authorization: bearer+Token
Content_type: application/json

Response: 422
“requestId”: “FEB11822-EB8E-44FF-BAAC-D9DA39F55527”,
“error”: {
“code”: “ConstraintViolationError”,
“message”: “The request is malformed.”,
“details”: [
“code”: “TargetTimeoutError”,
“target”: “https://17ecbf03.ngrok.io/v1/appresponse”,
“message”: “Upstream target timed out”,

please give the solution to solve this error…

Your target url is invalid or has errors.

Just check it on postman with POST request.
It has OK response.

At the time of app creation, that URL needs to be able to respond to a POST request “PING” challenge. This would indicate that the SmartThings servers did not receive a response at that URL.