@graceymanors I've just successfully downloaded a world and a set in my macOS (version 1.70) and Windows (1.67/Steam) installs, with no error messages. So the store isn't down overall, at least not at the moment.
I have a few questions for you. First, can you ever download anything at all right now? I often get the "you don't own this item" message the first time I try to download something, but refreshing the store page fixes it. If you can't download your store content even after refreshing, can you download something that's supposed to be free? For example, Riverview or one of the free holiday decor sets:
https://store.thesims3.com/setsProductDetails.html?productId=OFB-SIM3:44626
https://store.thesims3.com/setsProductDetails.html?productId=OFB-SIM3:46164
If you start the game, can you login at the Main Menu? If so, can you download anything from the Downloads Dashboard? (At the Main Menu, click the three dots and then select Open Downloads Dashboard.) Please let me know whether you even see any owned items listed there.
And I take it you're currently using an Origin install? If you have the patience, it would be interesting to know whether the Steam install lets you downloda content now. You could download only the base game, to save time, if you wanted.