If you own The Sims 3 on Steam but want to launch it via EA:
This is the most common issue in the Sims community. You bought a physical copy of The Sims 3 Pets from eBay or a garage sale. You try to install it, but the launcher says:
This is the most common issue in the Sims community. You bought a physical copy of The Sims 3 Pets from eBay or a garage sale. You try to install it, but the launcher says: sims 3 expansion pack codes