Add/Remove a fee based off cart existing in EDD

manditory-fee.php

<?php
function ck_add_remove_service_fee() {
        if ( ! class_exists( 'Easy_Digital_Downloads' ) ) {
                return;
        }
	
        $has_fee = EDD()->fees->get_fee( 'service-fee' );
        $items   = edd_get_cart_quantity();

        if ( ! empty( $items ) && ! $has_fee ) {

                $args = array(
                        'amount'      => 3,
                        'label'       => 'Service Fee',
                        'id'          => 'service-fee',
                        'type'        => 'fee',
                        'no_tax'      => false,
                );
                EDD()->fees->add_fee( $args );

        } elseif ( empty( $items ) && $has_fee ) {
                EDD()->fees->remove_fee( 'service-fee' );
        }
}
add_action( 'init', 'ck_add_remove_service_fee', 10, 2 );