You can sell more than just a hosting account, you may choose to sell domains with your hosting plans.
Navigate to Settings -> Products -> Products.
First, you need to create a hosting package and configure your domain services.
On the first page of the hosting package creation, you can see Include Additional Bundled Products. Select the Domain products option and then click the drop-down, and select the product group with your domains. By default, this will be Domain Services.
Save your changes, complete the rest of the package configuration, and you have allowed domains to be bundled with the hosting packages.