Hello, I am trying to register a new VoIP provider on my 3CX system. It registering ok and i am able to make a call but when i answer it i have no sound. On the logs it writes, 'No RTP packet were received'. On my try to debug this problem i found from the wireshark that when my 3CX registered with VoIP provider it shows 2 error '415 Unsupported media type' after 2 NOTIFY message ( i don't know if there is a connection with NOTIFY messages and 415 error). What can i do in order to solve this problem? Thanks.