NixOS - How to configure config property which is a type of types.lines

Question

Tried to install Flexget. On the Options website it shows that there is config defined here

How does it work? it says the type is types.lines. Tried to write some random text, but the config file is not created and the daemon fails to start.

Edit:

So here is my configs inside configuration.nix:

  services.flexget = {
    enable = true;
    config = "asdas\n asdas";
  };

and when I run sudo nixos-rebuild switch this is what happens:

building Nix...
building the system configuration...
NOT restarting the following changed units: systemd-fsck@dev-disk-by\x2dlabel-FuHua.service, systemd-fsck@dev-disk-by\x2duuid-25A4\x2d32EA.service
activating the configuration...
setting up /etc...
reloading user units for shalva...
setting up tmpfiles
reloading the following units: dbus.service
the following new units were started: flexget-runner.timer, flexget.service
warning: the following units failed: flexget-runner.service

× flexget-runner.service - FlexGet Runner
     Loaded: loaded (/etc/systemd/system/flexget-runner.service; linked; vendor preset: enabled)
     Active: failed (Result: exit-code) since Thu 2022-04-28 10:34:20 UTC; 129ms ago
TriggeredBy: ● flexget-runner.timer
    Process: 92136 ExecStart=/nix/store/1pdq67nfjw2mad5s679dfgm5h98bm4xm-flexget-3.1.153/bin/flexget -c /var/lib/deluge/flexget.yml execute (code=exited, status=217/USER)
   Main PID: 92136 (code=exited, status=217/USER)
         IP: 0B in, 0B out
        CPU: 799us

Apr 28 10:34:20 Lenovo-7200 systemd[1]: Started FlexGet Runner.
Apr 28 10:34:20 Lenovo-7200 systemd[92136]: flexget-runner.service: Failed to determine user credentials: No such process
Apr 28 10:34:20 Lenovo-7200 systemd[92136]: flexget-runner.service: Failed at step USER spawning /nix/store/1pdq67nfjw2mad5s679dfgm5h98bm4xm-flexget-3.1.153/bin/flexget: No such process
Apr 28 10:34:20 Lenovo-7200 systemd[1]: flexget-runner.service: Main process exited, code=exited, status=217/USER
Apr 28 10:34:20 Lenovo-7200 systemd[1]: flexget-runner.service: Failed with result 'exit-code'.
warning: error(s) occurred while switching to the new configuration

I htink the problem is in /nix/store/1pdq67nfjw2mad5s679dfgm5h98bm4xm-flexget-3.1.153/bin/flexget -c /var/lib/deluge/flexget.yml. Because the config file is not created. here is the output of it:

shalva in Lenovo-7200 in ~ took 16s
❯ /nix/store/1pdq67nfjw2mad5s679dfgm5h98bm4xm-flexget-3.1.153/bin/flexget -c /var/lib/deluge/flexget.yml
Could not instantiate manager: Config `/var/lib/deluge/flexget.yml` does not appear to be a file.

my expectation is that config = "asdas\n asdas"; should at least create config file at /var/lib/deluge/flexget.yml, right? I know it will still fail because it wont be valid config, but at least it should be created...