It seems to be a bit difficult to solve the E911 error with Verizon. I also got an E911 verification error when I entered a valid USPS address during the cellular setup process for my Apple watch. I created a ticket with Verizon. I had to check in manually on the status of my ticket. The ticket was resolved based on what the rep told me. Yet, the issue persists.
Linking other people's issues with the same errors here:
https://community.verizon.com/t5/forums/searchpage/tab/message?advanced=false&allow_punctuation=false&q=e911