WooCommerce's order status "Processing" actually means that it is completed but is intended for physical goods so that once the items are sent to the customer you can change order status to Completed. Tickera however, treats both statuses the same and yields the same result. Now, if you would still like to have your order status Completed instead of Processing for whatever reason, you can edit your products (ticket types) and check Virtual and Downloadable checkboxes within Product Data. That way, WooCommerce won't wait for you to change the order status but will change it as soon as the payment has been successfully completed.