Issue:
An order was placed in Shopify with three gift cards at $500 each for a total of $1500, but the Integration App imported only a quantity of one, and not three, therefore only showing a total of $500.
Resolution:
The NetSuite Sales Order rule for a gift certificate: Quantity is always one and cannot be increased if a Sales Order is placed having an item of type "GIFT CERTIFICATE".
Therefore, you must use the Inventory Item called a Gift Card.