Shameless Plug. How do you sell before you build if what you're building is a game?

I created https://diffudle.com/ a few months back without knowing what marketing, Idea Validation etc means. Wherever I posted, the overall sentiment was positive but the traffic to the site was still very low. Its peak was 1000 users but generally it hovered around 100 users a day. This is not enough to even sustain itself.

Lately, people told me that the game is not "that fun", I'd be very happy if I got this feedback earlier. How do I derisk this?

At least I coded it myself so saved 200k there :).