You need to configure the Extension to create the filter and set up the cron as well.
Kindly follow this documentation to configure the JA Mega filter.
It helps you to configure it for different extensions.
Sorry for the delay, due to weekend holidays there s limited support.
I checked your site and extension is not configured yet.
Please add cron Jon as mentioned in the documentation.
Also, add the extra field in the articles and add an image in the article via Joomla articles > image and links options. http://prntscr.com/ign6np http://prntscr.com/ign81w
Publish the module and it will show you range filter that you created, click on search will give the search results that are using extra fields.