I would like to get the% minimum and maximum% of a given region for freight calculation purposes for an e-commerce in Opencart .
The goal is to restrict free freight to the capital of Porto Alegre by having the CEP informed outside this region receive the freight calculations according to the values practiced by the Post Office and in case it is a CEP of Porto Alegre, apply free freight.
So, is there any documentation or rules on some website or even on the Post Office that allows you to determine the minimum and maximum zip codes of a certain region or some specification to do that?