OMV-extra Plugin error

Need someone help.
I am new in OMV. I tried to install OME-extra plugins.
see below error
Reading package lists...
Building dependency tree...
Reading state information...
The following additional packages will be installed:
dirmngr
Suggested packages:
dbus-user-session libpam-systemd pinentry-gnome3 tor
*************** Error ***************
Failed to execute command 'export PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin; export LANG=C; export DEBIAN_FRONTEND=noninteractive; apt-get --yes --allow-downgrades --allow-change-held-packages --fix-missing --allow-unauthenticated --reinstall install openmediavault-omvextrasorg 2>&1' with exit code '100': Reading package lists...
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[/quote]Building dependency tree...
Reading state information...
The following additional packages will be installed:
dirmngr
Suggested packages:
dbus-user-session libpam-systemd pinentry-gnome3 tor
The following NEW packages will be installed:
dirmngr openmediavault-omvextrasorg
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 595 kB/667 kB of archives.
After this operation, 1518 kB of additional disk space will be used.
Get:1 file:/var/cache/openmediavault/archives openmediavault-omvextrasorg 4.1.6 [71.6 kB]
Err:2 http://ftp.us.debian.org/debian stretch/main amd64 dirmngr amd64 2.1.18-8~deb9u1
Temporary failure resolving 'ftp.us.debian.org'
Unable to correct missing packages.
E: Failed to fetch http://ftp.us.debian.org/debia…2.1.18-8~deb9u1_amd64.deb Temporary failure resolving 'ftp.us.debian.org'
E: Aborting install.
<<< *************************************
*************** Error ***************

Thanks, it works.