Output Control - KOMPBV3

Hello

I created a new routine where I'm doing some validations, if they are meet then the message output will be available, the problem is that it is not working when the invoice is being created (VF01) because one validations is taking data from the table VBRP and this one is empty when the routine try to read it, so after some investigations I found that there is a structure that might help me KOMPBV3 but when I try to read it, is happening exactly the same problem, it is empty!!.

I need just to fields in order to do the validation which is Part number (MATNR) and Profit center (PRCTR), from the first item, I don't need all of them.

Do you have any idea why this structure is not filled up? do you know another way to get this fields?

Thanks in advance.

Hiram