brainCloud supports a wide range of popular in-app purchases, including Google Play, Apple, Facebook, Amazon, and Steam, etc.. In most cases, the purchase process is initiated through the corresponding IAP plugin that you need to download into your Unity project. Then, verify the receipt received from the purchase outcome with brainCloud by calling VerifyPurchase API. It should be noted that the necessary configuration for the IAP store must be set up in the brainCloud portal for your app, including the products section and platforms section. Some store integration examples are available on our documentation website -- https://docs.braincloudservers.com/learn/portal-tutorials/store-integration-google/
Hope this helps!