You don’t need to create android folder it’s already there.
This is what fixed my problem with IAP:
Go to Unreal Engine installation folder for me it’s O:\UnrealEngine\UE_4.16\Engine\Config\Android Open AndroidEngine file and just add:
[OnlineSubsystemGooglePlay.Store]
bSupportsInAppPurchasing=True
Remember to save the file before exiting. IAP will show after that.