Please follow the below steps:
1. Turn Airplane Mode on and off, and then dial again.
2. Calls are largely affected by the network. Try changing the network environment and call again.
3. Clear all background apps to ensure that the phone has enough memory.
4. Restart the phone and then enter the app, Make sure there is enough memory and try again.
5. Enter the app settings to clear the cached data and try again (we recommend you back up data before clearing).
If the issue persists, contact the Nothing Support Team for further assistance.