Update reject.php
Update reject.php

Due to https://github.com/sipgate/sipgate.io:
"Make sure to set application/xml in the Content-Type header of your response"
Drooids/sipgate.io,Drooids/sipgate.io,Drooids/sipgate.io,Drooids/sipgate.io,Drooids/sipgate.io,Drooids/sipgate.io,Drooids/sipgate.io,Drooids/sipgate.io,Drooids/sipgate.io