O2

I have a S21 Ultra on crontract and have bought a Galaxy Watch 3 LTE. I'd like to purchase an esim for the watch. I believe this is an additional £5 per month?I phoned customer services who told me I could do it through the my O2 app. I've had a look...

How does the e-sim on the galaxy watch work with O2? Does it just attach to an existing contract, or do you need to take out a seperate plan for it?