You're talking about this game?
https://eliell-vamp.itch.io/mine-find-the-story
It's only a demo.
"This is a short game with 3 endings which can all be finished in some minutes.
MINE is just the testing, Flower Letters is going to be the full game"
Reading the comments below the page, the demo was supposed to be free but the developer put a price tag just because they didn't want people to "get spoiled playing the demo"...very questionable logic but ok...
The pages for the demo and full game are separate. There's no guarantee to get the full game later after paying $15. So that's $15 for a few minutes of demo gameplay if anyone is thinking about this.