The VoIP Calls service uses Voice over Internet Protocol (VoIP) to deliver phone call messages through the IFTTT app (Android / iOS) to your mobile device. It’s available internationally and is an excellent alternative to the Phone Call service. All you need is the latest version of the IFTTT app.
If you're getting an error that states No VoIP devices registered, try logging out of the IFTTT app and back in. Some Android 8.0+ users have also fixed this problem by long pressing on the IFTTT app, selecting App info, and then making sure that the IFTTT app has access to all permissions. You may still need to log out and back in if the error message persists.
In 2018, the Chinese Ministry of Industry and Information Technology (MIIT) requested that CallKit functionality, which powers VoIP Calls, be deactivated in all apps available on the Chinese App Store. If you downloaded the IFTTT app from the Chinese App Store, then unfortunately VoIP Calls will not work for you.