Refused with 409 last_address if it is your only one — every future order would lose its origin while your listings stayed up. Refused with 409 default_address if it is the default and you have others; make another one default first.
using System.Net.Http;
using System.Net.Http.Headers;
var client = new HttpClient();
client.DefaultRequestHeaders.Authorization =
new AuthenticationHeaderValue("Bearer", "bk_test_YOUR_KEY");
var request = new HttpRequestMessage(
new HttpMethod("DELETE"),
"https://sandbox-api.biklo.com/v1/addresses/711");
var response = await client.SendAsync(request);
var json = await response.Content.ReadAsStringAsync();