While I was developing a custom tax provider, I ran into a pretty frustrating issue related to multiple tax lines and incorrect / unexpected tax total calculations. I outlined the issue in discord, before finding the solution: https://discord.com/channels/876835651130097704/1169705457804398662
After some digging, I found this issue from a while back: https://github.com/medusajs/medusa/pull/1262, where it states there is now a unique constraint on `item_id, code` and `shipping_method_id, code`. But, in the current documentation for creating a custom tax provider, it states these fields as part of the tax line items returned are optional.
If these `code` values are left out, it can cause tax lines to be applied multiple times (as seen here as well: https://github.com/medusajs/medusa/issues/1901)
I'm not entirely sure how this should be phrased in the documentation, so I just wanted to get this up and on your radar for resolution. If it ends up being that `code` truly should not be optional, I suspect some type definitions would need to change as well?
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