Sales Order credit check

Hi Gurus,

I'm new to FSCM. My requirement is that I have to implement the BADI UKM_CHECK_STEP so that a Sales Order is blocked when the Payment Term has value 'XXXX' even if the customer has sufficient available credit limit. Can anybody please suggest me how to do it? Do I have to create any credit rule? if yes, how?

Thanks in advance,

Sarif