Substitution rule for payment method

Hii Experts,

I have wrote an Substitution rule for a vendor for substituting payment method but when i put an entry through f-02 for that vendor, payment method field shows blank

call up point-2

prerequisite- Vendor (BSEG-LIFNR) and Co.code(BSEG-ANFBU)

Substitution- Pay. Method (BSEG-ZLSCH)

Prerequisite- vendor = 100005 and co.code=1991

Substitution- Pay. Method= N

System is not picking up any payment method is always showing blank.. Please guide me how can payment method can be substituted

Regards

Abhay