@nekonaja Okay, you could try installing Pets via disc, to see whether it works. If you get the disc authorization error, manually uninstall Island Paradise and reinstall it through Origin.
[Edit: These specific instructions are only for macOS. In Windows, sometimes installing via disc into an Origin-controlled install can make Origin recognize and load the disc-installed packs.]
https://bluebellflora.com/manually-uninstalling-an-expansion-or-stuff-pack-in-the-sims-3-for-mac/
You'd probably (unless you have a version of macOS older than El Capitan) also need to copy a folder from Ambitions into the folder for Island Paradise. The video in this thread shows how to do it:
Just try Pets first, because it's less complicated than installing Late Night. If you can't get it to work, you can use the manual uninstall guide to get rid of Pets.
