How to paint carpet?

fabric paint.

Hi Kay,

After looking at several rug painting projects, it became clear that you can use many kinds of paint successfully. Here's an example from a blogger who used regular wall paint. I've also seen acrylic, outdoor and spray paints used for this project. Take a look and see what you think. Check out some other rug stenciling projects as well, until you are comfortable with your paint choice. Wishing you the best.

https://craftingagreenworld.com/articles/how-to-stencil-a-rug/

If it's an olefin or polyolefin rug, any oil-based stains must be removed first.

You can use many different kinds of paint. It really depends on what your carpet is made of and if there's any stains that might bleed through the carpet.