I received a message in wordpress saying that there is an update available for this plugin (Backup & Restore Dropbox PRO) but that it can’t be updated
Backup & Restore Dropbox PRO license is available only for one domain. It means that automatic updates are available only for this very domain linked to purchased license. That is why, make sure that you try to update the plugin at the website for which you have purchased PRO license.
If you uploaded the PRO plugin version to the website for which you did not purchase the license, then the automatic updates will not work.