P-Series Inbound call Button Send VM / Send to VoiceMail not working

I’ve been trying to use the “Send VM” / “Send to Vmail” button on the Incoming Soft Key buttons but It does not work. I’m using a Sangoma P330 (fw 4.24.3), FreePBX 16.0.40.11, EndPoint Manager 16.0.86.30.

When.I receive a call, the “Send VM” softkey shows up. If I press it, the screen refreshes but nothing else is working. I’ve enabled all Logs, crated a Wireshark capture and noticed, that the phone sends a SIP/2.0 302 Moved Temporarily message to the server. The server even returns a SIP ACK but this message does not show up in the logs. You can access them at Seafile Server