Hosting services are allowing to add the extra domainls under the hosting cpanel of your account and you can easily add the addon domain from the cpanel of your hosting account with the help of below steps:
Steps required to add addon domain under cpanel :
1. Login into the cpanel of your hosting account.
2. Click on the Addon Domains option available under the Domains section of cpanel
3. Kindly insert the correct details under the Create an Addon Domains section and then need to clieck on Addon Domain