Zoiper FAQ and Troubleshooting
Zoiper Configuration
Please make sure to add Zoiper into the 'ALLOWED List' in Windows if being asked during or after installation.
1. Settings -> Accounts -> Add
2. Settings -> Advanced
For initial setup, please untick 'USE STUN'. This will be use for further troubleshooting depending on the local network.
Troubleshooting
Errors & Problems:
1. Error 408 Request Timeout
This error means that the phone did not receive a reply from the server (or there is no connectivity with it) and is common with new installation.
2. Incoming calls are not working
Issues related to incoming calls are a common problem with voice over IP.
Refer: https://www.zoiper.com/en/support/home/article/18/Incoming%20calls%20are%20not%20working#windows
3. SIP 503
The issue that you are experiencing might be because the DNS server does not reply at times. This could be a firewall issue.
4. Calls get disconnected after 30 seconds
This issue appears mostly because the session was not actually established and is in most cases network (NAT) related. This in most cases is because some routing devices / firewalls have built-in "SIP ALG"(Application-level gateway) functionality which is implemented to resolve NAT (Network Address Translation) issues, however the implementations are wrong and break SIP.
5. SIP 401 - Unauthorized.
SIP 401 - Unauthorized usually means that the request requires user authentication. Please check your username and password.