Rebates:Purchasing Group as optional field in MEB1

Hi gurus,

In our company, we would like to create a cross company rebate. However, our cross Purchasing Organization covers multiples Purchasing Groups.

We would like to change the mandatory Purchasing Group field in MEB1 to optional in order to select Agreement Type 1000, and them Purchasing Organization 9000 and Purchasing Group (blank) at Organizational Data pop-up.

Therefore, the settlement rebate will capture the entire POs of Purchasing Organization 9000 for our entire Purchasing Groups.

Could you tell us how to proceed?

Thanks in advance

Regards