To invite a multi-admin to the platform:
Sign into the CMS as a multi-admin
Go to "Accounts" (in sidebar)
Click on "Reseller accounts"
Click on "Invite New Reseller"
Enter your new multi-admin's name and email
Select role "Reseller"
Click Invite
Done! You've invited a new multi-admin to the platform. If you would like to upgrade an existing user to multi-admin, you can do so as a multi-admin via the User Management page.