As an independent designer, I use existing platforms to sell my patterns. Here is some info about my shops:
Ravelry is a lovely community where I have a group. It works with instant downloads and has a library where you can order and re-download your patterns whenever you want. When a pattern is updated, you’ll receive a message and can download the new version for free.
Etsy works with download links like Ravelry, but pattern updates are excluded.
Lovecrochet is my newest shop. It works with instant downloads like my other two shops. No pattern updates available.