This worked for me. Had to run these commands in the console as the “allow dropbox access” button gives error 400. Other posts have said to customize the dropbox settings form so you can enter an Access token generated from dropbox, but the menu–>customize button has been removed in newer versions of erpnext (leaving no way to enter the access token).
So from a command line, entering “bench console”, then the above solution solved my dropbox setup issues.
Thank you