If you struggle to create content for your coloring books, if you've spent more money than you can afford on PLR image packs, illustrators, or expensive software, and you still haven't made any money, then what I'm about to reveal is something you'll really need to pay attention to.
Creating a coloring book isn't an easy task.
It might be seen as a 'low content' book, but that content has to good. - So good that it can stand shoulder to shoulder with the other coloring books out there.
If it's not, well, you can forget any chance you have to make money from it.