@both in this thread ...
Need more info ... moodle version is? This contact form is a plugin? IF so what's the URL to the plugin in Moodle's Plugin site?
Also, if you were to turn on debugging all the way to developer, moodle might report something moodle specific. The error your sharing, 'Forbidden' ... is it a moodle error screen or is it a web service error screen?
'SoS', Ken