Processing subsequent messages only after current is successfully processed

Hello Experts,

I have the following requirement in my project. Can you please let me know of the best way to achieve this?

1) Source system sends XML file to PI

2) PI transforms the file to destination format (a BAPI call in this case)

3) PI makes a synchronus call to the BAPI and waits for BAPI response.

4) Once BAPI response indicates successful processing, proceeds to processing of subsequent messages.

The aim is to make sure that PI sends the next message only after it gets a confirmation that the current message is successfully processed.

- Michelle