Major Promotions/Custom Cart Items Issue?



We need to have a promotion not apply to custom items in a cart.

We are using custom items to manually add tax per several blog articles from Moltin, but they it seems that the promotional discount is being applied to the tax - which is not valid!

We have tried adding a second custom cart item with a negative value equal to the tax item, but the endpoint throws an error that “data.price.amount: Must be greater than or equal to 0”.

This seems like a major/critical issue but I can’t seem to find anything other than comments a year plus old on the “new” promotions api coming…what should we do?


Hi @adam.grohs

At the moment promotions are deducted from the overall cart total and custom cart items cannot be set with a negative value.

Just to make sure I understand correctly you wish to deduct the promotion value from the cart item but leave the tax as it is?

If you could give me a use case, that would be great in helping us gather data to pass to the product team to take into consideration.




We use a custom_item to record tax also. As tax is calculated by an outside service and applied to the cart after the promotion is applied, we cannot have the tax become “discounted” when it is added to the cart.



We have the exact same issue. It would be great with a feature where we could exclude certain items from being affected by the promotion discount and/or only have the promotion work on specific items in the cart.