# the only reason for which this error can be thrown is if invitation.send_response was called after the INVITE session was cancelled by the remote party
# the only reason for which this error can be thrown is if invitation.send_response was called after the INVITE session was cancelled by the remote party
self._invitation.send_response(488,extra_headers=[WarningHeader(399,engine.user_agent,'Both removing AND adding a media stream is currently not supported')])