Hi Gary,
Thanks for checking out Event Tickets Plus! For ticket sales, the checkout process and all payment processing are both handled through either WooCommerce or Easy Digital Downloads (it does not currently support WP Easycart). If you go with WooCommerce, you should be able to use an extension like Square for WooCommerce to integrate with your Square account.
Tickets are essentially WooCommerce simple products, so they usually play pretty well with WooCommerce extensions.
We do offer full refunds within 30 days of purchase, so if you’d like to test out Event Tickets Plus, feel free to do so! Please let me know if you have any other questions.
Thanks,
Jennifer