Webhooks API - Fix error handling for subscription activation

Description

We have fixed an issue in the Webhooks API where the activation of a subscription could fail due to an error in fetching the token needed for handshake authentication. Previously, this would result in a general 500 error. Now, the API will return a 424 HTTP status code if the token required for handshake authentication cannot be fetched during subscription activation.

The 424 HTTP status code was already used for handshake failures. With this change, authentication needed for the handshake is also treated as part of the handshake failure. From now on, instead of a general 500 error, a 424 error will be returned with the following response body:

{
  "errors": [
    {
      "code": "HANDSHAKE_FAILED",
      "message": "[Fallback] Problem with getting token for subscription: 41a50be7-3edd-42a1-a302-bc7fca51d7c5"
    }
  ]
}

Impact

This change is backward compatible, it does not introduce any new error codes, 424 was already returned in case of handshake failure.

References