ME_GUI_PO_CUST - How to implement custom header fields

I created an implementation for the badi ME_GUI_PO_CUST.

I see my custom fields in the custom tab that I created. I am not able to save custom fields data to the database ( EKKO ).

I used the method SET_DATA of IF_PURCHASE_ORDER_MM to save the custom fields but nothing is saved.

Any help is greatly appreciated.

Thanks,

Vijay