Use google play balance to buy gift card

To transfer your child's Google Play credits and YouTube gift card balance to a family manager's Google Pay account, click Transfer Pay Balance then fill out the form. If you do not see "Transfer Pay Balance" below, make sure you are signed in to the correct account.

You google play store balance can not be converted to cash or gift card, it can only be used to spend on the store on applications that needs to be bought.

You can use Google play balance for purchasing games, movies, books, newsstands, songs from the play store or in app purchases in games and other apps. You can not use this money in e-commerce websites like Amazon, Flipkart, Snapdeal etc.