If you receive Error 408 Request Time Out, when Zoiper cannot connect to the VoIP server. In that case either the server cannot receive the sent packages or the answer from the server cannot be received by Zoiper.
You may try to alter STUN. To activate it, please go to Settings -> Accounts -> Your registered account -> Network Settings -> Use STUN.
Please also make sure that the default ports used by Zoiper are not blocked from your Firewall or routing device. The ports used by Zoiper are as follows:
SIP port is 5060
IAX port is 4569 UDP
RTP port is 8000 and above UDP
Default STUN values are:
Server hostname/IP: stun.zoiper.com
Port: 3478 UDP/TCP
Refresh period: 30
If you using mobile internet connection, please contact your mobile connection provider.