Which watch in particular?
Some will take a sim whilst others don’t.
It isn’t usually compulsory for the watch to function either.
If you just want a PAYG sim you can order one free from here
https://www.o2.co.uk/shop/sim-cards/pay-as-you-go
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion.
This is not Customer Service so we are unable to help with account specific issues.Currently using:
Pixel 7a (O2 & Lyca), One Plus 6 (Sfr), iPhone 12 Pro Max (Vodafone)