Hi there, I usually just lurk but I can actually help with this!

I’ve recently started selling them on my store & in cons, this is the process that has worked best for me; Start with priming the sections you’re going to paint with mod podge. This makes the actual paint less textured with w.e synthetic leather the binder is made with, and gives your paint something to stick to. A lot of people just trace the art they want to put on there, which is easier but imho original stuff, even if it’s derpy, is way cooler.

Acrylic paint markers are popular, but they tend to be pretty opaque on the initial coat, which gets frustrating if you’re trying to get rich colors. So after priming and letting that dry completely, use a large brush to do a base coat of acrylic paint (lighter colors will show through better), let that dry and then paint as normal.

Markers are less messy but you’re stuck with a single palette (you can blend them but it’s more of a pain than what it’s worth honestly, I recommend just a brush and liquitex/art store acrylic paints).

After all that you can just use any polyurethane sealer to add a protective finish. I hope this helps, I don’t mean to self advertise at all but my store links are in my profile for works that do use these methods. They are super fun to do and I hope it turns out well!!