This is Size 1 from the Card Wallets pattern, but with a snap instead of the strap. One of the things I like about this pattern is you don't need any hardware or buttons, which keeps the supplies super simple at just fabric and interfacing. But of course, you can also use snaps or some other type of closure.
The red snap is a Snap Source size 24 long prong snap.
The finished wallet is available in my etsy shop.