Is this an internal - interdepartmental -communication? If so, then the message is clear. I've revised your two example sentences.
Please, confirm the balance on our invoice if the sample is approved.
As per Stella's information, Patrick shall remit 10,000.00 USD to us for PO #xxx. Please, tell us when we receive it so that I can issue an LC to the factory.
(note: There should not be a comma before "so" in this case.)
Student or Learner