Apple Music family login issue on inioasis G3

I’ve been trying to log into an inioasis G3, it comes with Apple Music preinstalled.

I’ve started an Apple Music family and I want to log my 10 year old into their own Apple account, she has her own ID but when I try to log in, it says for me to check the details (double and triple checked and they have been correct) or that my purchase can’t be processed.

Ive been able to log into to Apple Music using my own details, which make me think it’s an issue with using her login.

im trying to move away from Spotify, I was able to log her into her own child’s account on Spotify, so should be able to do it on Apple.

[Re-Titled by Moderator]

Original Title: Logging into inioasis G3