code: func (h *Client) ProductCouponCode(productCouponCode string) *Client {
  	h.productCouponCode = productCouponCode
  	h.productCouponCodeSet = true
  	return h
  }
docs: // The coupon code associated with a product. Product index
  // must be a positive integer between 1 and 200, inclusive.
  // For analytics.js the Enhanced Ecommerce plugin must be installed
  // before using this field.