You can find this section in HostBill Admin → Settings → Addons
Creating new addon is similar to creating new products. Click on "Create new addon" button and you will be redirected to configuration page. Provide a name for the addon, optionally you can add the description that will be displayed in client area cart and set-up the pricing. The addon can be free or paid, charged either one-off or on recurring basis with different billing cycles. Addons are billed separately.
Any time you want you can choose to hide the addon temporarily. To restore the addon simply tick the "Visible" box.
You can choose the Make this addon unique. If enabled your clients will not be able to order this addon twice for the same account.
You can enable this option if you want to charge accounts with this addon on specific date.
Under the automation tab you can set which actions and under what condition will be performed automatically by HostBill.
Under Emails tab you can define which email templates are used when this addon is provisioned.
There are four notifications option that can be assigned with template.
To be able to sell addons you will first need to attach them to one or more of your products. To do that go to Settings → Products & Services → Your Orderpage → Your Product → Components → Addons. Click on Assign addon(s) button and select your addon (or create a new one), click Add and save product configuration.
Your addon will be now available as additional option when clients select this product in cart.