It varies, some games require a purchase but most don't.I've just come round to seeing these games on inboxpounds. Do you have to put money into the games/apps when you have downloaded them? Or do you just literally play them? I'm a bit confused as to how inboxpounds tracks your progress on the games/apps
You click on the game on Inbox, screenshot the terms and then click on the Play store link. You download the game and then check your visited section to see if it shows up. If it's there you are good to go and can play the game.
Once you meet the terms and reach whatever milestone they require take another screenshot showing your level on the game and then check your ledger page to see if the game is pending. If it is not pending wait a day. If it still hasn't shown up click on the game in your visited section, click the button to contact support and submit whatever info they ask for. They will then credit you for the game.
I have had several games that showed in my visited section but didn't pend but I submit a customer service ticket with the evidence and I have always been paid.