If you are receiving a `STORE_PROBLEM` error on iOS when attempting a purchase. It's due to Apple's `/verifyReceipt` endpoint being down or not responding so RevenueCat is unable to validate the purchase.
In sandbox, these errors can be fairly common since the sandbox environment is not as robust as production. In production, expect these errors less often.
When these errors occur, the Purchases SDK will automatically retry validating the purchase on each app launch until a successful connection can be made with Apple - in most cases you don't need to do anything to resolve these errors.
Another option could be to display a user friendly error message letting them know there was an issue validating their purchase, but they can attempt to restore purchases.