So we’ve been dealing with this issue being sent to us by the reviewer.
We continue to find that your in-app purchase products exhibited one or more bugs when reviewed on iPad running iOS 15.7 on Wi-Fi.
Specifically, the Subscribe button was unresponsive when tapped and we were unable to verify the purchasing process for your in app purchase items.
Next Steps
When validating receipts on your server, your server needs to be able to handle a production-signed app getting its receipts from Apple’s test environment. The recommended approach is for your production server to always validate receipts against the production App Store first. If validation fails with the error code "Sandbox receipt used in production," you should validate against the test environment instead.
This is our first time releasing to app store. Should we ask the reviewer his/her appleID and add it as one of Sandbox testers?
We appreciate all of your feedbacks.