docs(create tax provider): tax line code required

[nickmonad]

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: #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: #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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[shahednasser]

Thank you for your contribution! I've added suggestions on how we can add notes explaining the unique constraint on item_id, code and shipping_method_id, code

[nickmonad]

@shahednasser Done!

[shahednasser]

LGTM! Thanks for your contribution!

[BorisKamp]

@shahednasser I ran into this issue as well. I created a custom tax provider but forgot to set the tax_code in the medusa interface:

This resulted in some order having trippled VAT lines. Why is this field not enforced as required in the medusa interface?

*edit: when I try to edit the rate, the VAT code is enforced. Somehow I ended up having null for the code after creating the new tax provider. Is this something you guys are aware of?

[BorisKamp]

See here on production, my code is empty....

[shahednasser]

Hi @BorisKamp can you open an issue with this?

[BorisKamp]

Hi @BorisKamp can you open an issue with this?

Hey! Done:
#7164