The Token endpoint URL may return an HTTP 403 error code when your API denies the access to the requested resource by VDP client.
I receive a HTTP 403 error when the Authenication information which I provide is sent to the service, but the Authenticated user is not permitted to perform the requested operation.
Therefore check your user permissions on the myob.com web page. Then select the option "Authorization" request header method for"" Request signing method to add HTTP header to the request.
You need to check if you are providing the correct header by refering to this page,[Myob headers](http://developer.myob.com/api/accountright/api-overview/headers/)
I hope this helps you!