Game installation failed. How do I solve this problem

There should be an error code (E1, E2, E3, etc.) for one of these cases, check here and see which one can help and try doing what the article recommends:
https://support.gog.com/hc/en-us/sections/360003883478-GOG-GALAXY-Error-codes?product=gog

I tried everything to fix this to no avail.
The game IS installed just fine, its Galaxy that fails itself.
I had to copy the game files to another place then remove the game from Galaxy completely to stop it from constantly downloading and failing OVER AND OVER AND OVER!