For in-app subscription I'm using this code (in Kotlin)
iabHelper.launchSubscriptionPurchaseFlow(act, "month", 1001, this@SubscriptionActivity, extraKey)
After this I'm making request to server for purchase verifying. For verification on server I'm using this code (in Go)
result, err := androidpublisher.Purchases.Subscriptions.Get(packageName, product, token).Do()
success := err == nil
How to get extraKey which I passed in app? I need it to know, which user made purchase