How to enable an segment value of COA to be mandatory for a responsibility

Hi All,

We have a requirement that one of the segment called Local Account of its COA need to be mandatory only at Payables responsibility level.

I tried creating a form customization at the payable distribution form where all the accounts are normally entered but it works only if the user goes to distribution form, if the user does not go to distribution form after entering th line details with default distribution details and click on validate , it validates the invoice, which means form customization is not working.

Where as we want the Invoice not to get validate if there is not Local account entered in distributions.