Even if you find a working key, the original 2005 PC version has issues:

If you want to play GTA San Andreas on PC without hunting for shady keys on Docplayer.net, here are your safe options:

The Trilogy – The Definitive Edition (includes GTA III, Vice City, and San Andreas) – ~$59.99 USD, but on sale for ~$29.99 frequently.
Note: This version has “remastered” graphics and quality-of-life changes but also had a buggy launch (now mostly patched).