It might work with other clients, but it’s the desktop one that’s trying to create a file on Dropbox, and Dropbox sends back this error. There’s not much we can do on Joplin side.
For anybody with these issues, I contacted Dropbox and they said they weren’t sure way was happening.
I managed to get past the issue by uninstalling the program, deleting the appdata, restarting the computer, and reinstalling. Then it came up with the option to link to the dropbox account again, and everything worked.