Add the sample code below to your child theme's functions.php file or in a site specific plugin.
<?php
//* Do NOT include the opening php tag
//* Update the messaging for the congratulations messaging that appears at the top of the thank you page
add_filter( 'FHEE__thank_you_page_overview_template__order_conf_desc', 'ee_change_thank_you_page_congratulations_messaging' );
function ee_change_thank_you_page_congratulations_messaging() {
return 'Your registration has been received! View your registration details by scrolling down.';
}
References:
http://eventespresso.com/wiki/ee4-thank-page-actions-filters-hooks/
https://eventespresso.com/topic/getting-thank-you-page-despite-credit-card-declined/
http://eventespresso.com/topic/onsite-gateway-incomplete-payment-if-form-resubmitted-after-cc-decline/
https://eventespresso.com/topic/changing-system-notifications/
http://eventespresso.com/topic/congratulations-message-on-check-payment/
http://eventespresso.com/topic/how-to-edit-the-ees_espresso_thank_you-default-message/
https://eventespresso.com/topic/editing-different-areas-of-registration-process/
See more recommendations for Event Espresso:
http://enzo12.com/labs/event-espresso/