custom fields don’t appear

Hello, in contact form 7 you can create a custom field, putting this in functions.php

add_action( ‘wpcf7_init’, ‘custom_add_form_tag_clock’ );

function custom_add_form_tag_clock() {
wpcf7_add_form_tag( ‘reloj’, ‘custom_clock_form_tag_handler’ ); // «reloj» es el tipo de etiqueta de formulario
}

function custom_clock_form_tag_handler( $tag ) {
return date_i18n( get_option( ‘time_format’ ) );
}

and this inside contact form 7 when making a form:

[reloj]

However, the CFDB7 extension is not picking up this field, which means that the fields cannot be customized. I wanted to know if it was my mistake? or do you have to activate any option? Or is that option simply not available? Thanks