I just downloaded and installed what I thought was a smartphone security key app *i.e., I can discard the physical security key that came with the game(, but instead, the app just keeps cycling through a bunch of numbers ceaselessly. I've tried entering those numbers physically into the PC desktop launcher, but they don&t work. Can anyone please explain this?

You must first remove the old Security Key, then you can set up the app as your new one.

Hello Jaren_Kincaid!

 

To me this does sound like your App isn't properly set up and connected with your account. To check whether your security key (SK) is connected try navigating to your account's SK page. If no SK is showing up try the steps documented in the official SK setup guide here.