MIR4 - booking of one invoice containing positive and negative positions via PO

Dear colleagues,

Is it possible to book an invoice in MIR4 that contains both debit and credit positions via PO? I know that you can click on the GL tab and specify the positions (DR or CR); however, in the PO tab/account assignment you can only type in positive numbers and you cannot choose between DR or CR.

Any suggestions on how to book such an invoice?

In advance many thanks for your help.

BR,

Achim