Why Can't My sims buy a resturant?

@Kengie830  It sounds like the pack might not have installed properly.  Try clearing Origin's cache:

https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/

and then repairing the game: open your Origin game library, right-click on the Sims 4 icon, and select Repair.

If that doesn't help, please make sure you have a folder for Dine Out in the game's installed files.  The folder is GP03, as in, Dine Out was the third game pack released.  Unless you changed the default install location in Origin, the full file path will be:

Program Files (x86)\Origin Games\The Sims 4

(Ignore the GP03 folder inside Delta; that's different.)  If you don't have that folder, you'll need to redownload the pack from Origin.