Hello Clara,
During backup or restore process running and also after this process was finished you can see step-by-step logging of this process on your screen, which is also written to log file on your hosting (in folder of your website).
Path to you log file is: /wp-content/plugins/dropbox-backup/tmp/<log-files>
In most cases there are described, what has gone wrong.
Please, send to us this files to e-mail address support(@]wpadm.com
For every additional information about your domain we will be appreciated. You can also use our support contact form at: https://www.wpadm.com/support
DO NOT POST YOUR PERSONAL INFORMATION IN THIS OPEN FORUM,
instead, please use our e-mail address support(@]wpadm.com or
support contact form at: https://www.wpadm.com/support
Thank you,
Dropbox Backup & Restore Support Team