Why isn’t the “discount code” function working when shipping to multiple addresses?

Since the multiple shipping address process requires us to calculate multiple tax rates and shipping rates for a single checkout, we have to build the checkout via Shopify’s API. The checkout that gets created does not support discount codes, however, we have rebuilt the discount code functionality, which gets inserted above the checkout button during the ship to multiple address process. This has to be enabled in Giftship’s settings:

Can't find the answer in our documentation?
Contact Support