go get golang.org/x/oauth2
go get golang.org/x/oauth2/google
go get google.golang.org/api/androidpublisher/v2

go get github.com/awa/go-iap/appstore
go get github.com/awa/go-iap/playstore
go get github.com/awa/go-iap/amazon

import(
    "github.com/awa/go-iap/appstore"
)

func main() {
	client := appstore.New()
	req := appstore.IAPRequest{
		ReceiptData: "your receipt data encoded by base64",
	}
	resp := &appstore.IAPResponse{}
	err := client.Verify(req, resp)
}

import(
    "golang.org/x/oauth2"

    "github.com/awa/go-iap/playstore"
)

func main() {
	// You need to prepare a public key for your Android app's in app billing
	// at https://console.developers.google.com.
	jsonKey, err := ioutil.ReadFile("jsonKey.json")
	if err != nil {
		log.Fatal(err)
	}

	client := playstore.New(jsonKey)
	resp, err := client.VerifySubscription("package", "subscriptionID", "purchaseToken")
}

import(
    "github.com/awa/go-iap/amazon"
)

func main() {
	client := amazon.New("developerSecret")

	resp, err := client.Verify("userID", "receiptID")
}