- Acorn TV channel subscriptions, as started inside the Apple TV app, are valid for watching in the Apple TV app on any of your devices, but not in the Acorn TV app. This would be administrated through your Apple ID account.
- Acorn TV subscriptions, as started inside the Acorn TV app on Apple devices, are valid for watching in the Acorn TV app on any of your Apple devices, but not in the Apple TV app, nor in the Acorn TV app on third party devices. This would be administrated through your Apple ID account.
- Acorn subscriptions, as started with Acorn directly (e.g. on the web), are valid for the Acorn TV app on any of your devices (any platform), as well as on the web, but not for the channels inside the Apple TV app. This option would have a dedicated Acorn TV account.
These types of subscriptions have different terms and conditions, different perks and limitations, and are mostly not exchangeable as such.
Acorn TV wouldn’t know your Apple ID account if you subscribed through Apple (but they could verify it if you provide credentials). Ask Acorn TV if they have options for watching on their site, when subscribed through a third party platform. Their answer might perhaps be different for Apple TV app channel subscribers and content provider app subscribers? I couldn’t find confirmation in their FAQ.
Apple TV HD, tvOS 11
Users are advised to keep their devices up-to-date for best support, features, fixes, performance, stability, and app compatibility. We’re on tvOS 16.3 now.
About Apple TV 4K and Apple TV HD software updates - Apple Support
Update your Apple TV - Apple Support