lifterlms_after_checkout_form.php

<?php // don't copy this line to your functions.php file

/**
 * Output custom html after the LifterLMS Checkout Form
 */
function my_custom_content() {
  
   echo '<h5>Secure Checkout secured by super secret enryption protocols!</h5>'; // add a little lock icon too, amirite?
  
}

// add the action
add_action( 'lifterlms_after_checkout_form', 'my_custom_content' );

lifterlms_before_checkout_form.php

<?php // don't copy this line to your functions.php file
/**
 * Output custom html after the LifterLMS Checkout Form
 */
function my_custom_content() {
  
   echo '<p>Enter your billing information below to continue!</p>'; // because we all know users get easily lost...
  
}
// add the action
add_action( 'lifterlms_before_checkout_form', 'my_custom_content' );