Gravity Forms coupon code - PayPal Standard- discount amount

// send non-negative numbers to PayPal Standard
add_filter('gform_paypal_query', 'update_paypal_query', 10, 3);
function update_paypal_query($query_string, $form, $entry){

    parse_str($query_string, $query);

    $items = 1;
    $amounts = array();

    // find out how many items are in the cart
    foreach($query as $key => $value){
        if( strpos($key,"item_name")!==false){
            $items++;
        }
    }

    $n = 1;// normal items

    // find out if any of those items are negative (discounts, coupons)
    for($i=1;$i<=$items;$i++){
        if($query['amount_' . $i] <= 0){

            $query['discount_amount_cart'] = $query['discount_amount_cart'] + abs($query['amount_' . $i]);

            // clear this discount item
            $query['item_name_' . $i] = '';
            $query['amount_' . $i]    = '';
            $query['quantity_' . $i]  = '';

        } else {
            // reassign the numbers so don't have any empties (or keep same if $n=$i)
            $query['item_name_' . $n] = $query['item_name_' . $i];
            $query['amount_' . $n]    = $query['amount_' . $i];
            $query['quantity_' . $n]  = $query['quantity_' . $i];

            $n++;
        }
    }
    for($a=$n;$a<=$items;$a++){
        //clear the remaining items so no duplicates
        $query['item_name_' . $a] = '';
        $query['amount_' . $a]    = '';
        $query['quantity_' . $a]  = '';
    }

    $query_string = http_build_query($query, '', '&');

    return '&' . $query_string;
}