Before you create an addon domain in cPanel you will need to point the domain nameservers to the server and wait for domain propagation. This can take up to 24 hours, however this usually takes much less time.
1. Log into your cPanel account.
2. In the “Domains” section, click on “Addon Domains” Icon.
3. Under the “Create an Addon Domain” option you should enter your addon domain name. This will auto-fill the remaining fields.
4. Click on the “Add Domain” button.
So long as your domain name has propagated to the server you should then see a green success message.