Reference Key 1 & Reference Key 2 in Outgoing Payment - F-53

Dear SAP Experts,

When I am posting Partial payment from F-53 against vendor invoice then in Vendor line item under MORE DATA field - Reference Key 1 & Reference Key 2 is editable and optional. partial-payment-f-53.png

But when I am posting full payment from F-53 then the same field is non-editable in Vendor line item.full-payment-f-53.png

I have checked after changing the field setting for Posting key and Field Status group of Vendor Recon. GL . I made those field optional in both OB41 and OBC4 but nothing is happening.

Do anyone encountered the same issue or anyone know how can we make this field optional in final payment also. Please suggest.

Regards,

Roy