Good day @felixmac,
Welcome to TPG Community!
If you are talking about the Apple Watch Series 3, which has an eSIM. It should be working with our TPG Mobile given that you have an Apple phone for your AW eSIM to sync the information from it.
If the eSIM of your AW is not functioning, you need to contact Apple/MAC support to check it.
I just want to correct myself with the information that I've provided.
As I've done some more research on our Mobile SIM plan, the Apple Watch is not yet supported as the eSIM technology is still being assessed. There's no timeframe that was given to us, but as soon as we received an update, we will post it here in our community.