API 'OKC_CONTRACT_PUB.UPDATE_CONTRACT_HEADER' is returning status 'U' with message count 0

Hi Team,
To update the service contract 'COGNOMEN' field in R12.1.3, we are using a standard api 'OKC_CONTRACT_PUB.UPDATE_CONTRACT_HEADER', But this api is returning status 'U' with message count 0.
Can you please help me.

Below are the script which we are using.

DECLARE
L_RETURN_STATUS   VARCHAR2(2) ;
l_msg_count       NUMBER;
l_msg_data        VARCHAR2(1000);
l_chrv_rec                       okc_contract_pvt.chrv_rec_type;
x_chrv_rec                       okc_contract_pvt.chrv_rec_type;
BEGIN

      l_chrv_rec.ID := 250162361190518738234376789142112915578;
      l_chrv_rec.object_version_number := 3;
      l_chrv_rec.date_signed := okc_api.g_miss_date;
      l_chrv_rec.start_date := okc_api.g_miss_date;