Dropbox authentication not working

This message started to appear on my Dashboard.
UpdraftPlus notice: Click here to authenticate your Dropbox account (you will not be able to back up to Dropbox without it).
When I click on it I get
http://MYSITE/wp-admin/options-general.php?page=updraftplus&action=updraftmethod-dropbox-auth&updraftplus_dropboxauth=doit
Which is blank.

In Updraft I get:
Warning: You do not appear to be authenticated with Dropbox (whilst deleting)

My backups are no longer going to my Dropbox, which has been successful for a number of months.

Any suggestions?

Thank you