On Apple TV can’t sign on to BritBox with pre-existing ID

Hello dddog.

Thank you for using Apple Support Communities. It sounds like you're experiencing sign in issues when using a specific third-party app on your Apple TV. If this is the case, we'd like to share some information with you.

Some apps might have a sign in option allowing you to sign into your already exisiting account. Other apps might require you to sign up for a subscription using your Apple ID that is linked to the device you're using. If you don't see a sign in option within the app you're trying to use, you can reach out to the app developers for assistance to see if they offer a sign in option for their app. The following link has more information on how to contact an app developer:

How to contact an app developer

Additionally, you can also try to use AirPlay to stream video or mirror your device's screen. For example, if you have an iPhone, you can use Safari to visit the specific website you want to mirror and use AirPlay to stream that content to your Apple TV. Just in case, the following link has more information:

Use AirPlay to stream video or mirror your device's screen

We hope this information is useful. Best of luck.

If try to use the Apple TV app Channel BritBox, then that will only accept Channel subscriptions started within the Apple TV app.

If your Apple TV box is 4th generation or later, then you can download the separate BritBox app and sign in with your existing account.

These are different types of subscriptions and not normally exchangeable. Some content providers allow you to create a new account from the Apple Channel subscription, to have it work outside the Apple TV app too.

Apple TV Channels FAQ: Services, pricing, availability, and everything else you need to know - Macworld

Subscribe to Apple TV channels in the Apple TV app - Apple Support

Also realized there are two Netflix, YouTubes, etc. Two layers of the same apps.

No, it doesn’t extend that far on the Apple TV box.

• Some services are only available as Apple TV app Channel (e.g. Apple TV+).
• Some services are available as Apple TV app Channel, or through a TV provider package, but not as a standalone service (e.g. Comedy Central).
• Some select services are available through their own separate app, and also as Apple TV app Channel (e.g. BritBox).
• Some services from their own separate app have their content linked to the Apple TV app, for showing their content in Watch Now and Up Next in the Apple TV app, and starting content from there. These will still need their own app for actual viewing (e.g. Disney+, Amazon Prime Video). Availability of supported apps in the Apple TV app - Apple Support
• Other (popular) content providers have chosen not to participate in Apple TV app support (e.g. Netflix).

Any smart apps on your LG are completely separate from this, but there will likely be an overlap of some services/apps.