If you are not able to make calls using Wi-Fi or Carrier data you will see a gear moving at the top right corner in the app or “Registering Error” at the bottom of the app. It is usually due to one of below reasons:
The internet connectivity transition has not occurred on the device. Close and restart the iPlum app.
In certain cases the port block or firewall set by your carrier or wi-fi provider may lead to connectivity issues. Close the app and try to change the source of internet or use a VPN app on your device. There are many VPN apps which you can find in iTunes or Google play.
Corporate users: If you have Cisco Firewall ASA 5505 family, make sure to switch off sip_policy. Configuration >> Firewall >> Service Policy Rules >> Inspection Default >> edit > Rules actions (tab) > Protocol Inspections (tab) > Sip (Uncheck it)