VeriFactu en .NET

using System.Net.Http.Json;

var http = new HttpClient { BaseAddress = new("https://api.verifactu.co/v1/") };
http.DefaultRequestHeaders.Authorization =
    new("Bearer", Environment.GetEnvironmentVariable("VERIFACTU_KEY"));

var factura = new {
    emisor   = new { nif = "B12345678" },
    numero   = "F2026/0184",
    fecha    = "2026-08-26",
    tipo     = "F1",
    // decimal, NUNCA double: los importes de una factura no
    // admiten el redondeo binario de un coma flotante.
    baseImponible = 100.00m,
    cuota    =   7.00m,
    total    = 107.00m,
    impuesto = "IGIC",
};

var req = new HttpRequestMessage(HttpMethod.Post, "registros") {
    Content = JsonContent.Create(factura)
};
req.Headers.Add("Idempotency-Key", "F2026/0184");

var res = await http.SendAsync(req);
var reg = await res.Content.ReadFromJsonAsync<JsonElement>();

if (!res.IsSuccessStatusCode)
    throw new Exception(reg.GetProperty("error")
                             .GetProperty("titulo").GetString());

Console.WriteLine(reg.GetProperty("huella").GetString());