The CIS feature needs to be toggled on to allow you to add CIS deductions to sales invoices.
Navigate to the Sales > Invoices menu.
Click on the Create invoice button.
Fill in the required details of the invoice.
Make sure to select one of the system generated CIS account codes in the Account drop down box (CIS labour revenue (20%) 1002001, CIS labour revenue (30%) 1002002 or CIS labour revenue (Gross) 1002003).
The CIS deduction should show in a preview below the Gross box.
Click on the Save button at the bottom.
Once the sales invoice has payment allocated then it will appear on the CIS suffered report based on the payment date.