In BUSY, you cannot pre define the lower rate of tds along with certificate number in party master. Further, you need to manually enable the lower rate applicability in voucher for particular party and update the tds percentage in tds deduction details window. You can follow these steps to post purchase voucher on lower rate of tds.
Step 1: Go to transaction section then click on purchase voucher and click on add tab.
Step 2: Now, Create the the purchase voucher with necessary details then apply tds along with tax in bill sundry.
Step 3: While save the voucher, you will get TDS deduction details window in which you need to enable the lower rate applicable and update reason with certificate no.
Step 4: Then, specify the tds percentage and save the voucher.