Tks for reporting that, i'll try to fix it soon.
About the puzzle, in the "basement" you can find this note:
spoiler:
Look at the symbol in the top left corner, it is a hint, also try to use it with the lines.
Hope this helps :))
Thanks, idk why i didn't thought of that. I finished it! it was very good, i'm just sad that it was so short lol