In StoreKit 2 the API to fetch in-app purchases is try await Product.products(for: subscriptionIDs).

Apple docs: The App Store may not recognize your product identifiers unless you meet the following criteria, as applicable:

Apple

• Agree to the latest Apple Developer Program License Agreement.
• Complete all the financial agreements described in the Agreements, Tax, and Banking Overview. When you renew your developer membership, see if you need to make updates to your agreements. When your developer membership expires, your financial agreements expire as well.
• Your app uses an explicit App ID.
• Clear the in-app purchases for sale in App Store Connect. See Set availability for in-app purchase.
• Modified in-app purchases are available to the App Store servers.
• The product identifier specified in App Store Connect matches the identifier used by the SKProductsRequest object in your app.
• Upload the content of your product to App Store Connect. See Upload in-app purchase content to App Store Connect.

Resources

• Apple docs: invalidProductIdentifiers
• Apple docs: products(for:)