If you are having issues with WiFi calling on your Android or iOS phone, make sure you have the IPSec (VPN) setting enabled on your router.
To enable, follow the steps below:
Step 1: Open a web browser and enter http://dlinkrouter.local. or the IP address of your router (http://192.168.0.1) into the address bar.
Step 2: Enter your password and click Log In.
Step 3: Hover over the Features tab and click Firewall.
Step 4: Click Advanced Settings and then enable IPSec (VPN). Click Save.