I guess there are multiple posts about audio but even after days/weeks/... of browsing knowledge bases etc.. and trying a lot of different things I cannot get it working.
I have a Yeastar S50, latest firmware.
There is one hardware phone connected (tiptel) and there are multiple remote extensions with a softphone app.
When I call from hardware phone to softphone I get sound, the other way around it does not work, one can not hear sound in the hardware phone.
The hardware setup is as follows:
provider with dynamic IP -> modem (no routing functionality) -> Mikrotik -> S50.
For NAT I tried with a hostname (DDNS) or the dynamic IP.
Forwarded ports are 5060UDP and 10000->12000UDP.
I also tried with a cloud voip provider and there I got audio working however, when the call was abandoned my phone kept ringing, quite annoying.