Learning In-App Billing at the Google Play Store ain't simple.
One of the hurdles is having to massage the old Eclipse sample project into AndroidStudio.
This repo contains the TrivialDrive project happily imported into AndroidStudio, equipped with all the needed Gradle jazz and upgraded to more recent Android versions. It's all ready to work upon, starting from requesting and inserting the API key.
Branch working-example contains the evolution up to the working app.
Clone and enjoy!