insert a new designated spot for Finance approval. With the format you have recommended, it looks like either Nui or Porn should sign. What I would like to see is Nui approves, then the PO goes to you for approval based on cash flow. Once you ok this, then the PO either comes to me or Khun Sarah for final approval. That way it is clear.
I am okay to discuss more details with you. Let me know na.