Update :Service contract header using API

Hi

I tried to update service contract header using    OKC_CONTRACT_PUB.UPDATE_CONTRACT_HEADER api but when i executed below script i am getting error message as 'U'

I am unable to understand where i am going wrong here. Could you please guide in correct path.

Thanks

Challa

DECLARE

L_Return_Status VARCHAR2(200);

  L_Msg_Count NUMBER;

L_Msg_Data VARCHAR2(200);

L_Msg_Index_Out NUMBER;

L_Data VARCHAR2(2000);

Header_Rec  okc_contract_pvt.chrv_rec_type;

Header_Out  okc_contract_pvt.chrv_rec_type;

BEGIN

------ Update CONTRACT HEADER ---------------------

Header_Rec.contract_number := 'LLNW-17197';

  Header_Rec.estimated_amount:=200;