As a person who also doesn't sell well: I've seen a lot of people say that they use discord servers and forums to advertise. I also think that uploading a new character as an advertisement usually works pretty well to attract attention from people scrolling through the recent character area, especially if you showcase some of your art as the avatar. And also, don't make your prices cheaper and cheaper, do what is worth your time and effort.
Take what I say with a grain of salt, and use the advice that works for you :)