Hi Zoiper Community.
This is a little technical and more of a bug report rather than question, but nevertheless I just want to know if anyone else experiencing the same problem.
Setup: Zoiper on Android Phone on cellular network (registers on host IP:portA) -> Host with public IP and NAT (port forward from external portA to internal SIP portB) -> PBX with internal IP (UDP SIP listens on portB).
That is, PBX is behind NAT listens on portB, but external port (portA) is a different. Regardless why it's like that (there are reasonable requirements), the setup is still legit.
Problem (discovered by a packet capture): Zoiper starts an INVITE to host:portA, gets an OK, but sends ACK to host:portB(!) which is dropped since not forwarded, so it won't reach PBX to start sending media.
Obviously, having destination and redirected ports to be the same solves the problem, but well, can't change the setup, can only change SIP client :-), and no offense, other ones indeed work correctly on the same phone.
Not allowed to send captures, and I do not have Android phone to repro at home, but I hope Zoiper developers could check this out.