The grey market (G2A, Kinguin, Eneba) is flooded with stolen or invalid keys for old games. You risk buying a key that was already redeemed or is region-locked to Russia/China.
If you own a and it doesn’t work on Steam, contact Sega support (current publisher). If you don’t have a key, the safest and cheapest option is to buy Company of Heroes Complete Pack on a Steam sale (often ~$10 or less), which includes Opposing Fronts . The grey market (G2A, Kinguin, Eneba) is flooded
: Check the back cover or the very first page of the printed manual. The Box/Case If you don’t have a key, the safest
If you have multiple keys (e.g., base game and expansion), activate them sequentially to unlock all campaigns. Common Issues and Support Guide :: Company of Heroes - Legacy Edition explained Common Issues and Support Guide :: Company of
A search for “company of heroes opposing fronts product key and retail code” often leads to shady “key generator” websites claiming to produce unlimited free keys.