How to restrict user creating Confirmation in SRM for ECC PO?

Hi SRM Gurus,

We are Classic scenario.

Users are able to post the confirmation for ECC back end PO(Created in ECC only).

I have checked the scn thread Can we post Confirmations in SRM for all Backen... | SCN and understood that he GR for ECC PO can be posted from SRM.

I want to know, how to restrict users creating GR for ECC PO from SRM?

Thanks in advance.

Best Regards,

Siddappa