cloudHQ Meeting Scheduler for Gmail has he intelligence to detect whether invitee has already scheduled the meeting or if the meeting invite is accessed by the person who created the invite.
This means that calendar invites will not work if the links are open in the same Google Chrome Browser in which the invite created (e.g. if you send an email from your email account to another account of you).
In order to properly test Meeting Scheduler for Gmail, you need to open your invite link using the browser in which you are not logged into cloudHQ. For example, open it in Google Chrome incognito window.
The suggested way to test Meeting Scheduler is to send the test emails with invites to your colleague or a friend.