Hi,
Can you share what are relevant configuration done for PO print with your PO message type!
Can you share your logic- why you are manually entering message type in ME22N for your PO ?
If no message type available in a PO - why you are trying for ME9F?
Cross check do you use same message type for new PO print and Changed PO print for print indicators 1 and 2 in fine tuned message type of PO segment.
Regards,
Biju K