How can I resolve 'FaceTime Activation unable to contact the FaceTime services' on iPhone XR?

Facetime uses international text messages to activate and operate. If you are using a supported carrier, there should be no charge for these and they should work if your carrier has your account properly provisioned.

If you are using an unsupported carrier, make sure international SMS messaging is part of your plan. You may be charged for those messages if using an unsupported carrier.