This just happened to me. AppleTV+ was working fine on my AppleTV and then today it didn’t recognize my subscription and wanted me to sign up for a trial account. Here’s how I ended up resolving the issue. On AppleTV go to settings > users and accounts > default user > manage subscriptions > sign in with Apple ID (I used the sign in with Apple device option). This seemed to reactivate my subscription on AppleTV and everything was restored. Good luck!
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