I ran into my own slew of issues getting my phone activated on verzion (t-mobile oneplus 7t, already carrier unlocked).
Here's my experience.
I went into the verizon store and they could not activate my phone based on its IMEI. That said, they took the sim from my pixel and popped it in and phone calls worked no issue. I could also send text, but could not receive them.
It took a few calls, but I eventually had to get to tier 2 tech support where they manually had to key in my device info so it could be activated on Verizon (wasn't in their device database). It was showing up as unknown device before then in their system and in the my verizon app. They said it would take 24-48 hours before it would be in the data base. About 24 hours later, I checked the My Verizon app and found it was now listed as a OnePlus 7T UNL and showed the device image.
After doing that, I had to call into support again and ask them to add Feature #83856 be added to the line (I had done this before on two other calls by requesting CDMA-Less be added, that didn't work as the techs had no clue what I was talking about and wanted to pawn me off onto One Plus support). Just ask for the feature number as they can look it up and add it to your line fairly easily. The moment they added that feature to my account, my texts started pouring in.
Hope this is helpful if you run into any similar issues that I did. I love this phone so far, hopefully they will streamline this setup in the future as I made multiple trips to verizon and called into support at least a dozen times before figuring out the best way to approach this. Expect tier 1 support to have no idea what you actually need 90% of the time and keep pushing for a T2 escalation if your device shows up as unknown in their system.
I've also read that if the device shows up in the system and you're having issues, getting a new sim may correct without having to worry about having features added/removed from the line as it should auto provision the features (according to T2 tech) when activating a new sim on a 1+ phone that is already in their system.