@BitterSweet-xo - It sounds like some sort of file type association has been made between sims3packs and the WA program file, which is totally unnecessary. We can try to fix that within Windows or the macOS (I'm assuming Windows here), but first it also sounds like your web browser is trying to "run" the file you want rather than just download it.
It's usually more efficient to just download these things, then set the browser aside and move them into the TS3 user game folder's Documents folder for the Launcher to read on its next startup. If your browser doesn't seem to have an option to download a file and leave it alone, perhaps try a different browser?
