I just tried it out again and G722 sounds like an old venyl lp from 1940
, which is played too slow
In other words, it's not compatible with (this) Fritz!Box SIP Server.
All other codes seem to work perfect.
Remembering back to 2007-8 when I first started using G.722. I had Polycom hard end points but had some trouble with some soft clients. The codec samples at 16 khz but the standard calls for the signaling to represent it as 8 khz. Some implementations ignored the deliberate irrationality of the standard, which created interop issues as you describe.