TDS calculation on concessional rate

Dear all,

Im facing the problem while calculating the concessional TDS rate for the particular vendors in invoice posting

I've given Exemption number, Exemption rate, Exemption reason, valid from and valid to dates in Vendor master. but its not calculating TDS on that invoice. i.e TDS amount is ZERO.AND not considering the exemption rate ALSO

Is there any settings need to done related to this or is there any SAP notes related to this kind of issues

thanks

regards

Nagesh