//your DI container
services.AddHttpClient<IViaCepClient, ViaCepClient>(client => { client.BaseAddress = new Uri("https://viacep.com.br/"); });

//then use in your domain service, handler, controller...
var viaCepClient = container.GetService<IViaCepClient>();
var result = await viaCepClient.SearchAsync("01001000", cancellationToken);

var result = new ViaCepClient().Search("01001000"); //searches for the postal code 01001-000
var address = result.Address; //Praça da Sé
var city = reuslt.City; //São Paulo
//do what you need with 'result' instance of ViaCEPResult.

var results = new ViaCepClient().Search("SP", "São Paulo", "Avenida Paulista"); //search for the Avenida Paulista in São Paulo / SP
foreach(var result in results){
    var address = result.Address;
    var neighborhood = result.Neighborhood;
    var zipCode = result.ZipCode;
    //do what you need with 'result' instance of ViaCEPResult.
}