Receiptvalidator is small library writen in GO lang. It can be used for simplified receipt validation (Instant App Purchases)
ATM libray is handling receipt validation for IOS, Amazon and Facebook.
Since external apis can be changed here is the info about suport for IOS, Amazon and Facebook
IOS - Validating Receipts With the App Store
AMAZON - Receipt Verification Service (RVS) (IAP v2.0)
FACEBOOK - Game payments Fulfillment
Pull requests and ideas for improvement are more than welcome.