Purchased products via a website

Your question is not very clear.

Use the app that the subscription is supporting. For example, if this is a subscription that offers additional features for app 123, open app 123 to view and use those features.

If you subscribed through a website, this won't be an Apple subscription and any support will have to come from the app developer/vendor directly. Apple won't have a record of it.

Purchases from Apple, and only from Apple, are listed in your purchase history. Others you simply have to remember or notice that an app does something more than just a trial or the free version enables.

Read this support article for directions about how to see your purchase history in the App Store or iTunes Store [mobile device, computer, or web] --> View your purchase history for the App Store and other Apple media services - Apple Support

- If Family Sharing is enabled, you can see your family members’ purchases. Select the Apple Account menu and choose a family member.

- Web: "To see charges from older purchases, you might need to look at your purchase history in Settings or the App Store."

- iOS device or computer: If you want to see purchases that you made more than 90 days prior, "tap Last 90 Days, then select a different date range."

If you see ‘itunes.com/bill‘ or an unfamiliar charge on your bank, credit card, or debit statement, click on this link --> If you see 'apple.com/bill' on your billing statement - Apple Support