mbuffer error message

[ext4xfs]

I was reviewing my znapzendzetup list when I noticed I'm getting errors like the following

root@server1:~# znapzendzetup edit storage/Backup
[2024-08-17 17:21:43.95085] [1150789] [info] WARNING: property 'src_mbuffer' not set on backup for storage/Backup, defaulting to 'off'
[2024-08-17 17:21:43.95099] [1150789] [info] WARNING: property 'src_mbuffer_size' not set on backup for storage/Backup, inheriting from legacy 'mbuffer_size': 1G
[2024-08-17 17:21:44.85822] [1150789] [info] WARNING: property 'dst_a_mbuffer' not set on backup for storage/Backup, inheriting path[:port] from legacy 'mbuffer': mbuffer
[2024-08-17 17:21:44.85834] [1150789] [info] WARNING: property 'dst_a_mbuffer_size' not set on backup for storage/Backup, inheriting from legacy 'mbuffer_size': 1G
Can't exec "command": No such file or directory at /opt/znapzend-0.23.2/lib/ZnapZend/ZFS.pm line 1554.
*** WARNING: executable 'mbuffer' does not exist on remote znapzenduser@server2 system, zfs receive can fail

Can't exec "command": No such file or directory at /opt/znapzend-0.23.2/lib/ZnapZend/ZFS.pm line 1554.
*** WARNING: executable 'mbuffer' does not exist on remote znapzenduser@server2 system, zfs receive can fail

However it works fine when I ssh:

root@server1:~# ssh znapzenduser@server2 mbuffer --version
mbuffer version R20210328
Copyright 2001-2021 - T. Maier-Komor
License: GPLv3 - see the LICENSE file
This program comes with ABSOLUTELY NO WARRANTY!!!
Donations via PayPal to thomas@maier-komor.de are welcome and support this work!

I'm using the rbash setup on the main readme. Is this just indicating it can't find it via the $PATH due to the rbash setup?