Hello Ronilo
Can you start by going through our Testing for Conflicts Guide https://theeventscalendar.com/knowledgebase/testing-for-conflicts/? I am wondering if you might have a plugin or theme conflict.
Begin by deactivating all other plugins, using a theme such as Twenty Seventeen https://wordpress.org/themes/twentyseventeen/, and see if the issue still persists.
Also, double check for any other updates available (Dashboard » Updates). It looks like your version of WordPress is a bit outdated.
Also, you will need to run the free Event Tickets before you can use Event Tickets Plus. Also, install an e-commerce plugin like WooCommerce or Easy Digital Downloads.
Read more about each option’s features and payment gateways.
Finally, when to you go Events » Settings » Licenses, do you see that your license activates for Event Tickets Plus? If not, you can access that either in your email when you purchased the plugin, or at My Account » Licenses.
Please let me know if the issue still persists after these tests.
Thanks
Courtney 🙂