We have been very very busy removing, improving and implementing back a lot of stuff in MoneyCoach lately that somehow we missed all the warnings about the API shutdown coming from the Dropbox guys. Lo and behold, yesterday they deprecated the old version of the API and we were caught with our pants down. However, this is not the time for justifications, but time for action!
We will be pushing an update very soon that fixes this along with some other ones and adds some user requested customizations.
If you try to use the Backup/Restore Dropbox now, there will be a 400 error message and nothing happens. Please do not try to do anything on your part, nothing you do will fix this. If you really need to use a backup system until the fix comes, you can always use iCloud or the CSV Export.
Stay tuned for more updates.