My subscription will expire, but I upgraded to Premium Forever
Apple sends out reminders when your app subscriptions are about to expire. If you upgraded to Premium Forever this can be confusing, however…
You don’t need to do anything. All is OK. You will not be charged. You will keep your Premium Forever status.
The subscription refers to the yearly subscription you had before you upgraded. The expiration date mentioned is the date that the subscription year would end. Premium Forever is not a subscription. It is a one time purchase that gives you access to Premium forever. It basically replaced the subscription once you got it. However Apple systems still let the yearly subscription run until expiration.