Ubisoft+ account linked to Xbox but unable to launch game

Hi

I subscribed to Ubisoft+ yesterday for my son's Xbox. I have linked the account to his Xbox. The Xbox app allowed me to download games to his Xbox absolutely fine but when launching them get an error 0x803F8001 asking to either insert disc or sign into the Xbox network or get it from Microsoft Store.

When checking Apps on the Xbox, Ubisoft+ doesnt say its owned but when opened, the option to purchase is no longer available.

It appears to me that the Xbox can see something happening with Ubisoft+ but not enough to be able to launch a game.

Please help, he's super keen to get going!

Thanks

:)