This is how I add an item. (It works)
$price = new \SquareConnect\Model\Money;
$price->setAmount((int)str_replace(".","", $_SESSION['shippingCost']));
$price->setCurrency('CAD');
//Create the line item and set details
$book = new \SquareConnect\Model\CreateOrderRequestLineItem;
$book->setName($_SESSION['language']['shipping']." (".$_SESSION['shippingService'].")");
//DESCRIPTION HERE
$book->setQuantity((string) count($_SESSION['products']));
$book->setBasePriceMoney($price);
array_push($lineItems, $book);
Here is a reference of what I want to achieve. Image