Hey JCDS2020,
Thanks for using Apple Support Communities! I understand you're seeing an error that your calls fail when attempting to use your Apple Watch to make a call. I definitely understand wanting to get this resolved, and I'm happy to help.
To start, I recommend resetting the network settings on the paired iPhone X. Please keep in mind that this erases all saved Wi-Fi networks and passwords, so have any necessary passwords available prior to performing this step.
Once you're ready you can do that in Settings > General > Reset > Reset Network Settings. When that is complete, please test if the same behavior continues.
If the issue is not resolved, let's unpairing your Apple Watch once more. This time, when pairing again do not use a backup, and test once more if the behavior continues.
Unpair and erase your Apple Watch
Set up your Apple Watch
If you're still getting the same error after those steps, reach out for further assistance here: Contact Support
Thanks again, and have a great day!