settlement_issue_on_accepted_default_effect

settlement_issue_on_accepted_default_effect = {
	save_scope_as = task_contract
	task_contract_taker = {
		set_variable = nomadic_migration_contract_$NUMBER$
		if = {
			limit = {
				location = root.task_contract_location
			}
			trigger_event = {
				id = mpo_contract_events.$ARRIVAL_ID$
			}
		}
		else = {
			start_travel_plan = {
				destination = root.task_contract_location
				on_arrival_event = mpo_contract_events.$ARRIVAL_ID$
				return_trip = yes
				on_travel_planner_cancel_event = mpo_contract_events.$RESET_ID$
			}
		}
	}
}

As written in game/common/scripted_effects/09_mpo_settlement_issue_effects.txt.