@ZLT Nice to see you around the community.
If that error message is popping up, then you do not have an active subscription under the Apple ID with which you are signed in on your iOS device.
You may have an active subscription under a different Apple ID.
If you know your other Apple ID, you can sign out of the one currently active on your iOS device, and sign in with a new one as follows:
If your device is running a version older than iOS 13:
From your iOS device Home Screen, tap on Settings.
Tap on iTunes & App Stores.
From the Store screen, tap on your Apple ID.
From the Apple ID dialog, tap on Sign Out.
Sign back in with your other Apple ID.
If your device is running iOS 13 or newer:
From your iOS device Home Screen, tap on Settings.
Tap on your Apple ID at the top of the page
Scroll down and tap Sign Out
Sign back in with your other Apple ID.
If you're unable to complete the steps I sent over, you'll need to contact the Apple support team for further assistance.
You can get in touch with the Apple support team here.
Hope this helps!
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