2.) Click the 'Add Site' button in the "Your Insty Sites in this Account" panel.
3.) Under Add or Select Domain, click the 'Add New Addon Domain' button.
4.) Then, type in the domain in 'Domain to Add', and click 'Add Domain'
5.) If successfull, you will get a message like the one listed below:
4.) Then, type in the domain in 'Domain to Add', and click 'Add Domain'
5.) If successfull, you will get a message like the one listed below: