Thank you for using Zoiper.
Error 408 is shown when the server was unable to produce a response to your register request within the suitable amount of time. If the error is shown for your SIP VoIP account, please try to disable all the features, that are not explicitly required by your provider. To do so open the "Preferences" window and go to "Accounts" tab. Select your SIP account and click on the "Advanced" sub-tab. Disable the following:
Then please use the drop-down menus and set "STUN" to "Do Not use STUN" and "MWI" to "Disabled".
If using Zoiper with WiFi, please make sure that the routing device 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
As for the STUN the default values are:
Server hostname/IP: stun.zoiper.com
Port: 3478 UDP/TCP
Refresh period: 30