It´s possible make backup of btrfs subvolume?

Hello, I am trying to make a backup of a btrfs subvolume, but it doesn´t backup anything. It does not give any error, simply says that there is any file or folder inside the backup.
O.S. Debian 10
Latest Urbackup Server and Client.

Thank you

have you tried to mount the subvolume and backup the relative path?