lib/Model/CheckoutOrder.php
public function setReference($reference)
    {
        if (!is_null($reference) && (strlen($reference) > 200)) {
            throw new \InvalidArgumentException('invalid length for $reference when calling CheckoutOrder., must be smaller than or equal to 200.');
        }

        $this->container['reference'] = $reference;

        return $this;
    }
public function setReference($reference)
    {
        if (!is_null($reference) && (strlen($reference) > 200)) {
            throw new \InvalidArgumentException('invalid length for $reference when calling CheckoutOrder., must be smaller than or equal to 200.');
        }

        $this->container['reference'] = $reference;

        return $this;
    }
Sets reference
@param string $reference The order id in the eCommerce system
@return $this