How to flow Material Write offs directly to costing based COPA

Dear All,

User wants to flow Stock write off to COPA on a real time Basis. I have configured additional assignment line in PA transfer structure with relevant Cost element as a source and new value field.

Also OKB9 is updated with cost element and i have selected Prf Seg for the same.

But when i am doing stock right off through MM Tcode MIGO/MB1A no COPA document is getting generated.

Any inputs friends as it is urgent issue!!!

Thanks & Regards

Sagar Chinchkar