Auto Release PO after Authorization

I created an event action to trigger after the final PO authorization step is completed. The event action should update the Purchase Order state from Planned to Released using Purchase_Order_API.Release_Order. The API is called but it  does not update the status. However I am able to get the PO status to update to Released if I revoke the Authorization step. Is there something blocking the PO to be Released when the final step is Authorized?