This link is very good.

1. Create a custom app that is TCP/UDP 5060.
2. Create and App-ID override policy for TCP 5060 and set it to this app.
3. Create and App-ID override policy for UDP 5060 and set it to this app.

I have seen this fix an issue where the call was made but audio didn't work for 10 seconds (also, dial back wasn't audible during calling).