Solution:
My guess would be you’re not defining the action for privileged and non-priviliged users. Do you have both
add_action( 'wp_ajax_ACTION', 'bookly_appo_Ajax' );
add_action( 'wp_ajax_nopriv_ACTION', 'bookly_appo_Ajax' );
In your php? wp_ajax_nopriv_ACTION
is probably what you’re missing.