The Developer Mode allow you to view all Posts, Terms, Users & Options custom meta data in a readable format. This feature is very useful to check what is actually saved in any WordPress Object.
To enable the Developer Mode, you’ll have to set the following constant in your theme functions.php
file:
// Developer Mode
define('ACFE_dev', true);
// OR:
add_action('acf/init', 'my_acf_init');
function my_acf_init(){
acfe_update_setting('dev', true);
// Or:
acf_update_setting('acfe/dev', true);
}