wpcf7_add_form_tag not working

I copy the code from cf7 doc to functions.php but not working

https://contactform7.com/2015/01/10/adding-a-custom-form-tag/

`add_action( ‘wpcf7_init’, ‘custom_add_form_tag_clock’ );

function custom_add_form_tag_clock() {
wpcf7_add_form_tag( ‘clock’, ‘custom_clock_form_tag_handler’ ); // “clock” is the type of the form-tag
}

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

Wordpress and Contact form 7 are all latest version.