Hi Georges,
Thanks for reaching out! I’d be happy to help you fix this.
Can you tell me which versions of The Events Calendar and Event Tickets Plus you’re using (or share your system information)? There may be some compatibility issues with older versions and WooCommerce 3.0.
You can try adding this snippet to your theme’s functions.php file (without the “<?php” tag at the top). If you’re not using a child theme already, it is highly recommended that you use one to make these types of changes so that they are not overwritten with future theme updates.
Let me know how it goes, and please let me know if you have any questions!