Programatically tax-exempt line item in the cart or checkout.

[jemHerrera]

Hello, 

We are a company that sells eyeglasses and sunglasses. I have been looking for a solution to this problem: 

If a Sunglass frame(product) is purchased by the customer without custom lenses(another product), charge tax to the Sunglass frame.
But if the Sunglass is purchased together with Custom lenses, don't charge tax to Product A.

I am fairly new to Shopify apps and have been reading API documentations, but so far I could not find a solution that can make this work. 

Here are my failed implementations so far:
1. I can't use discounts. Has to be taxed/not-taxed to show in our accounting.

2. I can't modify the product's "taxable" property in the admin during the order process. If multiple customers buy the same product at the same time, this may cause an issue.

3. I looked into Storefront api to edit cart line items, but there's no option to edit the "taxable" property of the line item (or maybe I just could not find it)

Creating a non-taxable version(or variant) of the Sunglass frame will be our last resort. It's not so neat because we basically need to duplicate every Sunglass frame that we have.

[SeanCJordan]

Hey @jemHerrera  -- we're running up against an almost freakishly similar issue here. Did you resolve this, and if so, how?

[jemHerrera]

We ended up working on a workaround which involves creating 2 versions of the product, where one variant is taxable while the other variant is non-taxable. We then used an app that automatically syncs inventory between the two, linking their inventory counts. Then we just programmed in the frontend as to which of the variants is being added to the cart based on certain conditions.
.