[WD My Passport Ultra] Can't backup in Dropbox

Since this year I haven’t been able to make use of the automatic backup in the WD Back Up app. Everytime the security copy begins, it says “preparing” and after 5 seconds it stops. Then a notification tells me that there’s a destination missing. I’ve updated the software, I’ve double checked there’s room in my dropbox account and still there’s the same error.

P.S.: I’m not sure of what are the english equivalents to the error names and such, since main language is spanish