If you bought a key that's not working, or you bought a retail copy and that key isn't working, contact support https://www.gog.com/support
GOG blocks keys that were purchased with stolen creditcards. A common practise for key resellers at key selling sites.
The only legit ways to get a GOG key are GOG.com, Humble Store and a new retail version.
man i knew that little old lady at the 7-11 was sketchy she said that she got it for her grandson and he recently came out of the closet so she decided not to give it to him...no man i got it on the humblebundle..says they are out of keys please be patient just not used to having to like buy a timeshare