Automations set to "0 days" won't trigger immediately because "0 days" aligns the due date with the moment of creation — so if the trigger time has already passed, the automation won't fire.
The fix: Use the Automation Added trigger instead. When an automation is active and added to a trip or contact — manually or via a workflow — it fires right away. No date offsets, no status toggling.
Note: the automation must be active when added for it to fire immediately.