Please try the following:
1. Turn Airplane Mode on and off, and then dial again.
2. Change the network environment and call again.
3. Clear all background apps to ensure your phone has enough memory.
4. Restart your phone and reopen the app.
5. Open the App Settings, clear the browser's cached data, and try again. Note that data will be lost after the browser clears the cache, so back up data before clearing.
If the issue persists, contact the Nothing Support Team for further assistance.