Please make sure to disable all features that are not explicitly required by your VoIP provider. To do so open the "Options" window and go to "Accounts" tab. Select your SIP account and click on the "Advanced" sub-tab. Disable the following:
Then set "STUN" to "Do Not use STUN".
If you are behind a routing device, please make sure it is not blocking ports used by Zoiper. The default ports used by Zoiper are:
SIP port is 5060
IAX port is 4569 UDP
RTP port is 8000 and above UDP
Default STUN vallues:
Server hostname/IP: stun.zoiper.com
Port: 3478 UDP/TCP
Refresh period: 30
