Fixed Price. "min" and "max".

Some gift cards have fixed prices, while others do not. If the “min” and “max” values of a product are the same, it indicates that the price of that product is FIXED, which is its face value. For instance, iTunes gift cards are available in amounts ranging from $5 to $500, whereas PlayStation gift card prices are fixed and available ONLY in amounts of $25, $100, and $500. 

If the “min” and “max” values of a product are NOT the same, you can select a number between the “min” and “max” in the API. For example, if the “min” price is $5 and the “max” price is $200, you can choose any amount between $5 and $200 when ordering a product.