This is very cool! Coming from a beginner, it might make the first few games easier if you added an extra setting that would start the puzzle with one or two numbers already filled in (like a typical sudoku), as that gives a natural starting point. Obviously, it may not be needed if you mainly develop this for yourself :)

I believe in the Puzzle I attempted, the solution was not unique: at the end, two numbers could be placed interchangeably (in my case, I could switch around all "1"s and "4"s and end up with just as valid a solution - that is, of course, unless I missed something :)

Very cool little puzzle, thank you for sharing!

I have absolutely no reference values for this kind of service, but 800 for small developers does sound fair to me (I suppose in most cases, one does not need to pay for more than a year…?) It’s really exciting to see this kind of solution and option for Godot, looking forward to seeing more projects on consoles!