If you have a Shapeways approved promo code (personal or sitewide), you can apply it to you cart after you've added your models there. The promo code can be applied on the right hand side section of https://www.shapeways.com/cart.
Auto Bulk Discounts for Versatile Plastic
When ordering models in Versatile Plastic at a quantity of 3 or more, an auto bulk discount will be applied. When successfully added, you will see "Bulk Discount applied" next to each eligible model and the discount total will be reflected under the "Order Summary" section.
Shapeways is looking to get you the best discount possible. Please note that promo codes are not stackable with our bulk pricing feature for Bulk SLS pricing.
Therefore, when you have a bulk versatile plastic discount applied to your cart and then you put in the seasonal/personal promo code, the system will automatically put in the highest discount available on Shapeways.