Can’t log into Apple TV app
My husband pays for the app monthly, but it won’t give us the option to log in, only to pay for a new subscription
iPhone 13 Pro, iOS 17
It doesn’t matter who pays for it, what matters is to which Apple Account the subscription is linked, or group member accounts in case of Family Sharing.
Users don’t pay for the app, but for the subscription content in it. The app itself is free.
See the subscriptions overview for your Apple Account - Apple (only for the original subscriber)
To have the subscription content be accessible in the Apple TV app on various devices, one needs to sign in. On third party devices, that can be done through the in-app Settings. Sign in to the Apple TV app - Apple TV app user guide for smart TVs and third party streaming devices - Apple Support
On what device and model do you have this issue?