Unable to create webhook subscription

I have tried to create the subscription using postman, am getting the below error.

Could someone help me to resolve this issue?

POST URL: https://platform.devtest.ringcentral.com/restapi/v1.0/subscription

Request JSON:

{

"eventFilters": [

"/restapi/v1.0/account/~/extension/~/message-store?direction=Inbound" ],

"deliveryMode":{

"transportType":"WebHook",

"address":"https://<mysitename>/auth/subs/v2.0/v/tkn";

}}

Response JSON:

{

"errorCode": "SUB-522",

"message": "WebHook responds with incorrect HTTP status. HTTP status is 500",

"errors": [

{

"errorCode": "SUB-522",

"message": "WebHook responds with incorrect HTTP status. HTTP status is 500",

"status": "500"

}

],

"status": "500"

}