How To Locate Your Purchase Receipt (Google)

When you purchase through Google Play, your transaction can be viewed by accessing your Google Play Account.

Visit Google Play, and log in to the Google account that made the purchase in question.
Under the "Activity" tab, you will see a list of all recent transactions. Click on the one you want to view.
Take a screenshot of the purchase details that appear on the right hand of the screen, including the "TRANSACTION ID".

For more useful information about getting the most from your Social Games experience, please visit http://smartsocialgamers.org/managing-social-games/