I recently used My Passport as a backup when Mojave was reinstalled onto my computer. Now when I’m trying to configure Time Machine (it’s saying it’s not configured) and select My Passport as the backup disk, I enter my my password to turn off encryption then get a message saying I’m unable to prepare the backup disk since it’s already reverting. Any help would be appreciated since I don’t want to erase the data already on it.
This issue might be due to the updation of macOS to Mojave OS. You need to reformat your My Passport before taking a bckup of important data files, into a compatible macOS Extended Journaled file format. Then configure Time Machine to get backup on your mac.