How to execute shipping calculation at product level without state selection

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I have a two part question regarding shipping. I'm based in Brazil.

Shipping rates vary wildly here because of the distances involved. Therefore ecommerce sites here all offer shipping calculation at the product page level, not just cart or checkout level.

I can't seem to find an api that offers this option: request a shipping calculation based on a single product (or multiple if more than 1 item is selected. Is there an api for this?

In Brazil zipcodes are exact. If you enter a correct zipcode, a selection of state is unnecessary. However, Shopify requires this, creating a below par user experience, at the very least below what competing platforms offer here. Country I can select by default, but the state will depend on the zipcode. What I'm trying now is just adding a random state, in the hope that zipcode will take priority over manual state input. But I would prefer to just disable this state validation.