Hi there,
If you encounter fatal error when activating Tickera plugin, please make sure that PHP version on your website is at least 5.6. Also, if fatal error occurs when trying to activate plugin immediately upon installation (by clicking on Activate button on the plugin installation page), try navigating to Plugins area and then activating from there.
Finally, if neither of these helps and you are still stuck with fatal error, shoot us an email with your FTP and WP admin access so we troubleshoot what might be wrong or, if you are installing it locally, provide us with as many details as possible about your local server and WordPress installation.
Cheers,
Tickera Team