The same happens to me, and same if I use this apple link to redeem a code https://apps.apple.com/redeem?id=YourAppAppleID&code=OfferCode.
But the same code works just fine if I redeem in App Store > Profile > Redeem a gift card or code.
I believe this is a bug, that happens for specific developers/users, and that a ticket should be created.
asx
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