@Dawood_Aijaz - gotcha, just making sure everything in the request was squared away. Are you able to create webhooks on other resources? How did you check for existing webhooks on your resource? If you haven’t already, you can call this endpoint with a GET request and pass in your workspace and resource ID to confirm what’s already been set up there.
Is this the same issue you had in this thread from a year ago? If so, was it ever resolved?