This has been an ongoing deal for a while, so I apologize if it's already been posted. But I haven't seen it here, and just recently found out about it myself.
That's right, it's the mothafuckin Cash App
Cash App sends you a debit card linked to your installation of their mobile app. You use the app to attach a "Boost" (dumb way of saying "coupon") to the debit card. For as long as I've been using it, about a month now, they've always had 15% off "boosts" for PSN and XBL with an unlimited number of uses. So you throw $50 onto the app, choose the PSN boost on the app, pay on PSN with your cashapp debit card, and observe after-the-fact that only $42.50 was deducted from your account instead of the full $50 you spent on PSN.
Not gonna soil this good forum with a referral link, so here's their homepage: https://cash.app/