My Sims 3 Steam Code isn't working

@MeowHorse13  Once the Steam copy of Sims 3 is showing in your EA App account, the Store should work too.  Does Sims 3 show up in your EA account because you previously registered it from Steam, or because you own a separate copy?  If the former, then I'm not sure why the Store isn't working, but also, you won't be able to register your Steam code a second time.  If it's the latter, then yes, you'd need to add your Steam code to the EA App, so the problem is not with the Store or your account but the code itself.

At any rate, you'll need to contact EA customer support to ask what's wrong with the code.  Take a screenshot of your Steam library showing the base game CD Key, and upload it when you submit the help request.

https://help.ea.com/en/contact-us/

I'd strongly suggest using live chat rather than email.  If you don't see the option, change the location in your browser window to U.S. or U.K., or choose a slightly different category of issue.

And let me know if you don't get anywhere with support.

They said it was a sync error between EA and Steam and is apparently a common issue everywhere right now. They said to try again later(I assume every few days?) as it's being worked on. :/

@MeowHorse13  There's no reason to feel dumb.  It's not usually necessary to login to the launcher when installing Store content.  I have a Steam install too, and I never login.

Thanks for the update though.  I'm not sure why the Store is asking you to sign into the launcher, but if that's all it takes to get around the issue, that's a reasonable workaround.