iPhone XR: Wi-fi Calling Stopped working

Tim, Thanks for the reply. I don't think either of these things apply. I've got a great connection. Tested this morning at 250 Mb. Zero packet loss from East Coast to West Coast. Has been working just fine up to now and no router settings have changed. Searching about this feature (for any carrier) shows it is a problem for every single one of them, so this leads me to believe it's an software implementation problem. Notice that the error message from iOS is dead wrong. It says that I have no Wifi connection. But I do have a connection and it works fine in any other context.

Tim, with respect "You do not have a network connection" is false. I do have a network connection and a really good one. It may be the carrier (having a history with AT&T, it seems sort of probable) but if you search for the problem, it's looks like no carrier has figured out to do it right and the really terrible thing is that Apple has given no way to diagnose the problem. And that is just a poor situation for the consumer that Apple needs to consider. If something doesn't work, there should be a way to figure out exactly why it's not working.

Thanks. Yes. Turned Wifi off and on. Turn Airplane mode off and on. Turned Wifi Calling off and on. Did a hard reset of the phone. A solution would be my first choice, but seeing from this and several other posts that there is no way to actually diagnose the problem, ranting is all we have left.

More information: There is another iPhone XR in the house. I checked and WiFi calling is working on it. Same exact model bought at the same time. Both connected to same Wifi device, connected to same ISP. Both the running the same exact version of iOS. As I said before, I hard reset the device, turned every imagineable feature (Wifi Calling, Airplane mode, Wifi, Bluetooth, etc etc.) on and off. Still no Wifi calling.