Yes its one time for android, if you’re earning money with ads or purchases, google will take 1/3 of that amount, then you will have to figure out taxes on your own and there’s also some special policies for selling online goods in India, but if you’re just making apps - its one time fee to be able to upload them to google play store, or you can just distribute with froid/github for free, which is a great route as well
Worth to note that their audio quality and anc is worse than competition noticeably. So its quality vs environment