I have a linux URbackup server backing up to a windows host for storage. This is working fine and files are being created.
I have the option turned on to backup the internal DB, and the directory exists and a new backup_server.db file is updated with todays date, it’s always 0 bytes.
Looked at the source code and errors during the database backup are logged at info level unfortunately. Can you turn down the logging level to info and then have a look at the log file? (See this post)