Sync problem

After upgrading my Dropbox to 1TB, syncing between my Mac and iPhone is working, but there is a problem on my iPad I do not understand. When I tap the cloud icon to start a sync, at first I got a message saying I had an invalid encryption key. I edited the sync location, found the place to enter the key, and did so.Saved it. I’m quite sure I have the right one.

Tapping the cloud icon again, I get this message: “That actioni is not authorized. Please ensure that you are authenticated.”


Checking the cloud icon, it seems to be processing, and tapping it shows it in the process of downloading a bunch of stuff. So, what was that bit about authentication?