I did sell on Amazon. I have Amazon books live on KDP right now, actually but, I've had the most success with Gumroad. With Amazon, I usually hear from other sellers that it either really works or it doesn't. For me, it hasn't. But honestly, I haven't done any marketing, which is a big part of the process. So, I haven't given it a really fair shot, really. I haven't given up on Amazon. I sold on Sendowl and had some success but, nothing like what I've experienced on Gumroad.