Use the Secure Code emailed to you to activate your Subscription.
If you didn't receive the email with the Secure Code then check your Spam folder.
The Secure Code is only valid for 1 hour, post that you will need to initiate a new secure code request.
When a user from a domain has activated his trial license, another user from the same domain name cannot sign up for trial automatically. They will have to send an email to email@example.com and request for the same.