Using Zoiper for Linux with my VoIP provider causes no problems whatsoever. Using the same settings in the same LAN from the same IP address behind the same router but with Zoiper for Windows (free or Biz - no difference) leads into a strange behaviour.
After starting Zoiper and setting up the account for the first time, everything works okay. Exiting and starting Zoiper again leads to the complete loss of outbound audio, the other party can hear me, however. If I now deregister and change something senseless in the account setup, e.g. Caller ID (does not matter what I put there, VoIP provider does not use this info at all) and register again: everything ok again.
Exit and start Zoiper again: outbound audio gone. Deregister, change anything, register: everything ok.
This purely Windows behaviour does not depend on ipv4 or ipv6 or firewall on or off; it's always reproducable. It shows on Windows 7 Pro, Window 10 Home and Windows 10 Pro.
Starting same PC with Linux and Zoiper works just fine again.
rport, stun settings or using and forwarding other ports produces the same results.
But no such problems with Zoiper Classic on Windows. Which does not fulfill other requirements, however.
Any idea, please!