The maximum quantity limit is a feature implemented by many games by default. I think it's a feature that Playfab should have.
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Add 'UpdateEmailAddress' to API -- Currently you have to do this manually
PlayFab validation for rewarded adverts
Allow generate coupon via API (for example, gifting)
Make items more intuitive in terms of accessing certain elements
Optional longer coupon codes when used as a "game key"
Game Key Management - A RedeemCoupon extension + mgmt console