If you need testers you don’t tell them to pay for your service and you’ll refund them, you give them free access to your service. Otherwise this appears to be just another low level scam attempt where testers buy ads and then you disappear without refunding. I get you want people to test this for you, but if testing the payment system is what you’re going for, maybe you should send funds yourself instead of asking others to do so for you and expect you to send them their money back.