Apple Watch Cellular - Connection to the server was lost

Original post from someone else:

I have a watch that won’t connect..

When I set up the watch with service and try to sync the watch to my phone, it pairs but when I try to set up cellular plan to sync the plan to the app, it says: “Connection Failed. The connection to the server was lost. Please try again later.”

But I work for the company that I have service with as a tech support, and I’ve changed the EID I’ve even changed watches. Reset network settings on my phone and have ran every troubleshoot there is. I’ve even gotten a new watch! But still I get this message. What can I do? Two watches and a new plan and still can’t connect.

I have exactly the same problem with my watch. See attached screenshot. I've spoken to my service provider as well. The service has been activated, but I can't get past this screen. My watch has been reset as well. Only thing I have not done is resetting my iPhone. All devices are up to date and network settings have been updated as well. Devices are Apple Watch Series 6 Cellular and iPhone 12 Pro Max.