Google play cards never redeem

I got a few google play gift cards from Mistplay and now google wants verification for the cards that i earned (proof of purchase). I've been doing this for years and this is the first time I've experienced this. I have several cards adding up to 25 usd that are now under google review (they can do what they want). This might set people back on offers, hence why I'm posting this as a heads up. I'm sticking with the visa/mastercard gift cards from now on, idk why i was trying to be cute.