Custom fee for COD (if free shipping is not available)

add_action( 'woocommerce_cart_calculate_fees', 'custom_handling_fee' );
function custom_handling_fee ( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    $chosen_payment_id = WC()->session->get('chosen_payment_method');

    if ( empty( $chosen_payment_id ) )
        return;

    $subtotal = $cart->subtotal;

    // SETTINGS: Here set in the array the (payment Id) / (fee cost) pairs
    $targeted_payment_ids = array(
        'cod' => 17, // Fixed fee
    );
    $minimum_amount = 500; // Amount needed for free shipping

    // Loop through defined payment Ids array
    if ( $subtotal < $minimum_amount ) {
        foreach ( $targeted_payment_ids as $payment_id => $fee_cost ) {
            if ( $chosen_payment_id === $payment_id) {
                $cart->add_fee( __('Plaćanje pouzećem', 'woocommerce'), $fee_cost, true );
            }
        }
     }
}