3rd Party PO with Zero value

Hi,

I trying convert 3rd Part PR in to the PO. I want select the line Item as "Free Item" (Zero value). system is not allowing to mark the Check box (Free Item Check)..it is in Gray mode.

it is happing only for 3rd Prty item.

Could you help on this.

I would appreciate your help.

Warm regards,

Dhamodar