Question about "juju backup" and the checksum

Was looking at “juju backup” and it reported something like this (some lines excluded)

backup format version: 1  
juju version:          3.0.0
base:                  ubuntu@22.04
machine ID:            0
checksum:              Z2A/TuDzTeoPUOEdyK3GMcXBrlA=
checksum format:       SHA-1, base64 encoded

Downloaded to juju-backup-20221116-191854.tar.gz

But I’m not getting the backup file to match the reported checksum above.

I’ve tried

sha1sum -t juju-backup-20221116-191854.tar.gz | basenc --base64 
sha1sum -b juju-backup-20221116-191854.tar.gz | basenc --base64

and none create a checksum that equals Z2A/TuDzTeoPUOEdyK3GMcXBrlA=

Does anyone know what the “SHA1/base64 encoded” checksum for what juju create-backup refers to?