Make sure you have deactivated the FREE plugin and installed and activated the PREMIUM PLUGIN. If you have both active at the same time the FREE plugin will run and you wont get premium features.
You should have got an email with a licence and a download link.
If for any reason the email did not arrive you can get the download and licences by logging in to your account at https://fullworksplugins.com/account using the email you registered with, request a new password if you never had one. If you get stuck then contact us.
If you have some how deactivated your licence key ( e.g. deactivated and deleted the plugin and re-installed it ) you can reactivate simply on this page yourdomain.com/wp-admin/options-general.php?page=widget-for-eventbrite-api-settings-account and click on the blue activate button on the bottom right of account details.