If you’d like to fasten a strap with a “rivet button”, as shown here, as is seen on a lot of pairs of Cydwoq shoes, you can order “replacement pairs” for $5.00 from Cydwoq, look for Rivet Attachment Metal Button.
If you are making the shoes yourself, you can be sure you have made the strap the correct length so it fits nicely over the “button”. I’ll experiment by ordering a pair of these to use on a pair of shoes. Buttons like this that I’ve seen in leather working catalogs don’t screw tight enough for shoe-leather usage, but since Cydwoq shoes are made with thinner leather, I anticipate these will work fine!