This usually means the OBB folder is in the wrong place or renamed incorrectly. Ensure it is exactly com.rockstargames.gtasa .
Extract it. You will see a folder named com.rockstargames.gtasa . Move (Cut/Copy) this entire folder to the following path: Internal Storage > Android > obb Step 5: Launch and Play Download Gta San Andreas Apk - Obb - Mod V2.00-