I've implemented In-App-Purchase feature for the app and tested it both in local and TestFlight builds using several devices in different counties and everything works fine. I receive SKProduct and make puchase with receipt validation. But review team rejected the app 3 times in a row with the same message that there is no purchase to make (SKProductsRequest returns no valid SKProduct). Are there any ways to reproduce their environment or investigate the issue?
Check that you have signed your banking contracts and that you have marked the IAPs 'cleared for sale'. Also be sure that you have added a screenshot on App Store Connect and that you have attached the IAPs to the binary.
The fact that "...review team rejected the app" suggests that your IAPs were not submitted or they are marked 'needs developer action'. You need to clear that.