I got Sims 3 via Origin Access recently. I can play the game without logging on, but I get prompted to log on each time I start the game. However, when I go through the registration process, the form will not let me create a persona, and if I use an existing one (MassEffectxxxxxxxxxxx where xxx is lots of numbers) the completion button is still greyed out.
@duGarbandier When you say you get prompted to login, do you mean at the launcher and/or the Main Menu? Both are asking for your Origin account credentials. If you can't login with that info, try clearing Internet Explorer's cache. Even if you never use it, the launcher does for some purposes. (So does the Sims 3 store.) Be sure to uncheck the box to preserve data for favorites.
Eventually I noticed that the browser being launched by the Launcher was Internet Explorer. So I copied the URL and opened it using Chrome. Yada yada, I'm in now.
I don't trust Edge to work properly with everything these days, never mind IE.