How can I apply custom tax amounts to line items on an order in Shopify?

[mdunbavanCub202]

Hello,

We have a tax service api that allows us to send order line items up, an order source address and other data. This api then returns tax rates back for each line item whether that is VAT or Us Sales tax.

Obviously we know that if we are giving a UK source address to the api we return VAT result and we know that we are already including VAT in the price in Shopify so naturally we would not add that into the price but obviously display the tax amount included.

We don't however include sales tax for US orders so we need to be able to edit those line items and add the amount of tax back onto that included in the order and we then need to make sure that the customer pays that in the checkout. Also within that we have scenarios where some products are taxable and others aren't such as non-prescription lenses.

I suppose I want to know if this is doable using the GraphQL api and a custom shopify app integrated within the store. Are there major limitations for us doing this? Is Shopify setup to allow this?

[hsdonkin_lazer]

This is something I'm also interested in, but for a separate reason: historical order import.

Unfortunately it seems like tax lines for orders are dynamically computed at the moment of order creation, and there's no way to create an order and manually override the tax line.