Why are discounts not similar in Cart and Checkout when multiple discounts are applied?
One of the most essential benefits that Vitals offers is that our apps are built to function flawlessly with each other.
Take these 2 products listed on our demo store, which are both listed with different prices and different volume discounts when 2 or more are bought:
When 2 pieces of each product are added to the cart, our algorithm receives cart contents, identifies the discounts eligible for the products, and displays each discount for which the cart is eligible.
Shopify only supports a single discount code to be added at checkout. We're generating a discount code that makes sure that the exact combination of products is added to checkout that discounts the total value by that exact amount.
However, when that discount code is added to checkout, it is applied to Shopify proportionally to each eligible product's total value. Let's look at the cart above - a total discount of $5.41 + $8.42 = $13.83 is added to a total value of $78.18, which is approximately 17.7%. Given that it's applied proportionally, the discount shown in the cart for the 2 Short sleeve kids t-shirt is $7.45, which is exactly 17.7% of $42.10. The same for the other product - as you can see in the below screenshot of the checkout.
If a different product is added to checkout that's not eligible for the discount, it will not appear discounted in the checkout. We instruct Shopify to apply the discount to eligible items, but we can't enforce the value to be applied on each line item.