warning message in include zxm06u43
I am new to abap and i have never done enhancement before.Now, the requirement is that i want to display a warning message for a particular vendor category whenever the purchase order is created .
I found that to display a warning message before creating a PO we use exit_sapmm06e_12 > zxm06u43 include .( please tell me if i am wrong )
now, i want to know the steps to make changes in this include so that i can display the warning message.
Thanks in advance,