Auto-balance HTML for ContactForm 7

mu-plugin-cf7-auto-balance-form-html.php

<?php

/**
 * WHY? Because invalid HTML will break a page, will break visible form feedback.
 * Still, WHY? Well, you are right, CF7 should do this all on their own.
 */

add_action( 'wpcf7_save_contact_form', function(WPCF7_ContactForm $contact_form) {
  // this is an action, contact_form not given as pointer, so get the pointer from CF7;
  $cf = WPCF7_ContactForm::get_current();
  
  // get the properties, we need to change the form
	$props = $cf->get_properties();
  
  // auto-balance HTML for the form data
	$props['form'] = force_balance_tags( $props['form'] );
  
  // save the new properties
	$cf->set_properties($props);
});