This will help with subscription issues.
The first thing to try is double touch the home button on the device and reboot the device.
Apple tracks your subscription using your Apple ID. I have no access to subscription information.
First verify your subscription using this:
If you have a current subscription, pressing Restore or Subscribe should activate the subscription with no extra charge. If Restore doesn't do fix it, hit Subscribe.
If you have in app purchases restrictions turned on this can block the subscription.
Screen time can block subscription purchase or renewal:
I have noticed that a bad data connection can also cause issue with the subscription. You might try on WiFi.
In some cases it is necessary to delete the app and re-install it. The reasons for this are complicated.
(Users have been ignoring the advice below, much to everyones discomfort. The subscription system is not mine, it's Apple's and sometimes it just needs a reset. please do not ignore the steps in this FAQ. Each steps is here for a reason.)
In some cases you need to sign out of your Apple account and sign back in. Settings->iTunes & App Store.
View last 90 days of Apple charges and or report a problem with a subscription.