Why doesn't targetctl (python) see the saveconfig.json file in the systemd service?

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In sytstemd service targetctl (/nix/store/a1f9s815jflz86j63r8wzgvkr0gmxcr2-python3.9-rtslib-2.1.74/bin/targetctl) not found saveconfig.json file for restore targets iscsi after reboot nixos 21.11: service for restore in /etc/nixos/configuration.nix:

systemd.services.foo = {
enable=true;
description="iscsi start";
unitConfig = {
Type = "simple";
};
serviceConfig = {
User="root";
Group="root";
RemainAfterExit="yes";
ExecStart = "/root/script.sh";
};
wantedBy = ["multi-user.target"];
after = ["sys-kernel-config.mount network.target local-fs.target"];
};

script.sh:

#!/nix/store/p0s6lymjfi6d9sdx253912zryvw2d2fr-system-path/bin/sh
if [[ -s /root/saveconfig.json ]]
then
    echo "saveconfig.json exist"
else
    echo "saveconfig.json not exist"
fi
/nix/store/a1f9s815jflz86j63r8wzgvkr0gmxcr2-python3.9-rtslib-2.1.74/bin/targetctl restore /root/saveconfig.json

systemctl status foo.service:

● foo.service - iscsi start
     Loaded: loaded (/etc/systemd/system/foo.service; enabled; vendor preset: enabled)
     Active: active (exited) since Wed 2022-05-25 05:02:40 UTC; 27s ago
    Process: 818 ExecStart=/root/script.sh (code=exited, status=0/SUCCESS)
   Main PID: 818 (code=exited, status=0/SUCCESS)
         IP: 0B in, 0B out
        CPU: 126ms

May 25 05:02:40 nixos systemd[1]: Started iscsi start.
May 25 05:02:40 nixos script.sh[818]: saveconfig.json exist
May 25 05:02:40 nixos script.sh[820]: No saved config file at /root/saveconfig.json, ok, exiting

/etc/systemd/system/foo.service:

[Unit]
After=sys-kernel-config.mount network.target local-fs.target
Description=iscsi start
Type=simple

[Service]
Environment="LOCALE_ARCHIVE=/nix/store/y9ga08zc1hif37f72vfmi8lys7ki5lmc-glibc-locales-2.33-123/lib/locale/locale-archive"
Environment="PATH=/nix/store/ndkb1hkd009fch9dkzs31p9b7sa61s61-coreutils-9.0/bin:/nix/store/majf16rlq7ggn18p3k380hv66gmpqhc9-findutils-4.8.0/bin:/nix/store/hq0dj7mrf3nn4xppyg4ypmm2jb2cpfla-gnugrep-3.7/bin:/nix/store/zym2hpmaz22x0rc8x09d862g1gr22djw-gnused-4.8/bin:/nix/store/kmxd50nhkzhm8iwscmi05h9kj3p45ghg-systemd-249.7/bin:/nix/store/ndkb1hkd009fch9dkzs31p9b7sa61s61-coreutils-9.0/sbin:/nix/store/majf16rlq7ggn18p3k380hv66gmpqhc9-findutils-4.8.0/sbin:/nix/store/hq0dj7mrf3nn4xppyg4ypmm2jb2cpfla-gnugrep-3.7/sbin:/nix/store/zym2hpmaz22x0rc8x09d862g1gr22djw-gnused-4.8/sbin:/nix/store/kmxd50nhkzhm8iwscmi05h9kj3p45ghg-systemd-249.7/sbin"
Environment="TZDIR=/nix/store/izida45x5809k8pxx7nwnlnvfgi3k6q3-tzdata-2022a/share/zoneinfo"



ExecStart=/root/script.sh
Group=root
RemainAfterExit=yes
User=root

I saw a similar question: Python script as systemd service but I didn 't understand about

adding with pkgs; [utillinux kmod]; to systemd.services.iscsi-target.path , so it’s in the services $PATH, too.
How to solve the problem? Thanks.