Server-related causes:
Not enough disk space
Server runs out of memory
Server has been placed behind a firewall and cannot be accessed
The backup is taking too long to be created and eventually times out
Trying to back up a non-existent directory or one that has been deleted
Trying to back up a directory which you don’t have permissions to read
Invalid/changed server credentials (host, port, username, ssh key, or password)
Storage-related causes:
A problem uploading backup to remote storage
Invalid/changed storage credentials (key, secret, region, or bucket)
Database-related causes:
Trying to back up an empty database
Invalid/changed database credentials (db host, db port, db username, db password, or db name)