Built a photo to coloring page tool. Struggling to identify the first paying niche.

I built ReliveInColor, a product that turns real photos into coloring pages and puzzles. The build was straightforward, but I’m now stuck on the harder part: who the first paying users should be.

I can imagine parents, teachers, therapists, gift buyers, or creatives all using it, but that’s also the problem. If you were starting from zero, which niche would you test first and where would you try to reach them?