Is your server responding to the challenge with the challenge? This payload is sent to the URL on creation, and your server must send it back in the response. If you don’t your webhook creation fails.

{

  "challenge": "VROo2eDe5EZIN0jtf6qwpVX-Th6mxeh8MvmnqfZKELEVnOSyZjgPPbNENzy4jQWS71pHKHRe7eYyf-FU4bDRmw"

}

Thanks @anon29275264 !

That was the issue, I added code to handle challenge and now I can create my webhook 😉

Thank you @anon29275264!