Prepare a piece of leather (about 8 cm x 7 cm) and a piece of denim (about 9 cm x 15 cm) with Spring Snap Fastener.
Here we use the LeatherCraftTools.com kit "Okayama Denim x Leather <Coin Wallet Kit>".

Finish the flesh side and edge of the leather parts.

Fold back about 5 mm from the end of the main body (denim part) and crimp it with Double Sided Adhesive Tape.

Make it the same width as the closing flap (leather part).

Fold back about 6 mm from the end of the main body (denim part) and crimp it with Double Sided Adhesive Tape.

Firmly hold down the folded parts (especially the corners) with a roller, etc.

Sew only one side of the folded part.
Here, it has been machine sewed with VINYMO <MBT> Polyester Machine Thread (#8 color:171).

Overlap the closing flap 15 to 20 mm over the main body and attach it to the body with Double Sided Adhesive Tape.
Then sew the closing flap and the main body together.

Make a round hole (approx. 5.4 mm in diameter) in the desired position on the closing flap for attaching the Spring Snap Fastener with Round Hole Punch.

Bend the main body and the closing flap, and mark the position of the Spring Snap Fastener on the main body.

Make a round hole (about 2.5 mm in diameter) in the marked part of the main body to attach the Spring Snap Fastener by Round Hole Punch.

Use the Spring Snap Setter Large to attach the male part of the Spring Snap Fastener to the main body.

Fold the main body in two and temporarily fix them with Double Sided Adhesive Tape.

Sew both ends of the main body together.

Use the Spring Snap Setter Large to attach the female part of the Spring Snap Fastener to the closing flap.

Check and make sure the Spring Snap Fastener stay in place and shape the whole thing, then it is done.