Add a domain on its own...

[rivermobster]

If you haven't already, create the client by navigating to Go to Clients > Add New Client.

On the client summary page, click the "Add New Order" link in the Products/Services panel.

In the first box, the client will be preselected. Begin by choosing the payment gateway you want the client to pay with and set the Order Status dropdown to “Active”.  Ensure all tick boxes for “order confirmation”, “generate invoice” and “send email” are unchecked so the user is not emailed about the order you are adding.

In the Product/Service aera, leave the dropdown menu set at None & the Billing Cycle dropdown menu set at Monthly.

in the Domain Registration field Select “Registration”.

Enter the domain in the Domain text field (even though you aren't intending to register it today)

Choose the number of years you next want the client to be invoiced for at the time of renewal and tick any addons the user has for their domain.

Click the submit button to add the order to WHMCS.

You will now be shown the order screen summarizing the details of the order you just added.

Now as the final step, you must go to the domain's information page to enter the correct next due and expiry dates as well as selecting the registrar the domain is registered with if using one of the built-in registrars. To do this, from the order screen, click on the link in the Item column of the items ordered - this will take you straight to the details screen.