I've been having this issue for two months despite factory reset and everything. Basically, my Pixel Watch will not connect to LTE no matter what I do. The notification keeps showing up that "Phone is not allowed for voice" and in the SIM Status menu, it reads as follows

Signal Strength: -83 dBm 56 asu

Network type: LTE

Service state: Out of service

Roaming: Not Roaming

Network State: Disconnected

Phone Number: Blank

My provider is Google Fi and the mobile data was working until I did a reset on the watch a few months back. It actually worked last week somehow but has since gone back to not working. I've tried deleting the eSIM and reading it, deleting the watch off of my Fi account and adding it back, and pretty much everything short of factory resetting my Pixel 7 Pro. I'm at my wits end with this and Google Support has been largely unhelpful.

Update (10/18/23)

So I originally obtained the watch from a friend who works for T-Mobile. From my research, I have seen that the Pixel Watch obtained through T-Mobile is carrier locked. The message "Phone is not allowed for voice" is usually only run into with carrier locked phones, so I can only assume that T-Mobile locked the watch despite saying they didn't. I reset the watch, my phone, deleted esim, and nothing worked. Be careful obtaining watches from carriers, just buy direct from Google instead.