When you buy a Google Play gift card, you can use it to buy content on Google Play. If you have a gift card, use the gift card or promotional code to find out how to use it. 

Gift cards are convenient because you can add money to your Google Play account without needing a credit or debit card. They are also often used as gifts for those who want to access and enjoy various digital content and services available through Google Play. 

Google Gift Card has no fee/expiration date. Refunded Google Play amount will be credited back to the Google Play Gift Card balance for future use under these terms of service unless otherwise required by law. 

Gift cards cannot be exchanged for cash or other cards, cannot be recharged or refunded, cannot be combined with non-Google Play balances on your Google Payments account, and cannot be resold, exchanged, or transferred except as required by law. If your order to be paid with your Gift Card balance exceeds your Gift Card balance, the transaction will be refused.  

Google Play Check the balance(https://paids.google.com) 

Online Support (https://support.google.com/googleplay/go/cardhelp)