To be able to receive incoming calls, your account has to be registered with the VoIp server,
When looking at the dialpad the account name will be colored green if the account is registered.
Sometimes the incoming calls will not reach Zoiper even if the account is registered correctly. The most common causes for this issue are:
Your account is registered somewhere else.
Some servers do not support multiple registrations. You need to make sure that your server supports multiple registrations before registering your account from more than one device or softphone .
When using Zoiper behind a NAT router you could experience a NAT timeout.
Try reducing the RE-REGISTRATION time for the affected account.
Run Zoiper for Android, go to Config, then open Accounts -. select your the affected account and scroll down to Network Settings.
If using UDP transport type, set the re-registration time to 30s. In case you are using TCP transport type for your account, set the re-registration time to 600s.