The CIS feature needs to be toggled on to allow you to add CIS deductions to bills.
The supplier used on the bill must also be updated as a subcontractor.
Navigate to the Purchases > Bills menu.
Click on the Create bill button.
Fill in the required details of the bill.
Make sure to select one of the system generated CIS account codes in the Account drop-down box (CIS labour cost (20%) 2002001, CIS labour cost (30%) 2002002 or CIS labour cost (Gross) 2002003).
The CIS deduction should show in a preview below the Gross box.
Click on the Save button at the bottom.
Once the bill has payment allocated to it, then it will appear on the CIS return based on the payment date.