How to send "passive" check results from an external Script

Hi Stevie, hi Michi,
sorry but I am a little bit confused.
My Script (which is running on a remote Host) is running well and send Status OK or Staus NOK after execution every 24hours. This runs well and the iciinga-master display the Status well.
But what I need is the Status “unknown” if my script is not running (can`t send Status of e.g. Network or Server Problem).
Means if the check on the icinga-master is older than 24hour I would like the Status “unknown”.

Here my Service and my api post:
The interval is changed for test!

apply Service “backup_lb” {

check_command = “dummy”
max_check_attempts = “1”
check_interval = 60s
retry_interval = 70s
enable_active_checks = true

assign where host.vars.backup_lb == “yes”

vars.dummy_state = “1”
vars.dummy_text = “No Status received since 24hours”
import DirectorOverrideTemplate
}

curl -k -s -u icingaweb2:xxxxx -H ‘Accept: application/json’ -X POST ‘https://icinga-mon-master:5665/v1/actions/process-check-result’ -d '{ “attrs”: { “ttl” :“90” }, “type”: “Service”, “filter”: “host.name==“Passive_Checks” && service.name==“backup_lb””, “exit_status”: 0, “plugin_output”: “[OK] Dies ist ein Test \n”