4 weeks ago
@Mabel916 Open your Origin game library, click on the Sims 3 icon, select More > Expansion Packs, and scroll down to where Late Night is listed. What does the orange button say? (Download, Buy Now, etc.) If it says Download, you can do so. If it says Installed or Play, then the question is why the pack isn't showing in the launcher. In this case, start by clearing Origin's cache, and if that doesn't help, uninstalling Origin "the hard way" and reinstalling.
If this doesn't fix the issue, it's possible that your pack has been deactivated. This could be a mistake, but if you bought Late Night through an unauthorized third-party seller, it's possible you received a bad code, and EA has now blocked it. The only way to find out if this is what's happened, and to correct any mistake, is to contact EA customer support and ask about the status of your pack.