By purchasing a GooglePlay gift card You confirm you are familiar with the latest policy from Google in which:
1. Users can't redeem Gift Cards that are purchased outside (United states) the country or region of residence; (you must be present in United states with local IP address no VPN or proxy)
2. Google may require more information from a suspicious user before a user can redeem the GooglePlay Gift Card code. Since this is not related to the used/invalid code issue - full responsibility for the purchase & its consequences rests with the buyer.