EU VAT validation in .NET / C#

using System.Net.Http.Headers;
using System.Text.Json;
using System.Text.Json.Serialization;

public record VATResult(
  [property: JsonPropertyName("valid")]           bool Valid,
  [property: JsonPropertyName("status")]          string Status,
  [property: JsonPropertyName("company_name")]    string? CompanyName,
  [property: JsonPropertyName("company_address")] string? CompanyAddress
);

// In your service — register HttpClient via IHttpClientFactory in prod
using var http = new HttpClient();
http.DefaultRequestHeaders.Authorization =
  new AuthenticationHeaderValue("Bearer",
    Environment.GetEnvironmentVariable("TAXID_API_KEY"));

var url = $"http://localhost:3000/api/v1/validate/DE/DE123456789";
var json = await http.GetStringAsync(url);
var result = JsonSerializer.Deserialize<VATResult>(json)!;

if (result.Valid)
  Console.WriteLine($"Valid EU business: {result.CompanyName}");
else if (result.Status == "service_unavailable")
  Console.WriteLine("VIES unavailable — retry later");
else
  Console.WriteLine("Invalid VAT number");

curl "http://localhost:3000/api/v1/validate/DE/DE123456789" \
  -H "Authorization: Bearer $TAXID_API_KEY"

# {
#   "valid": true,
#   "status": "active",
#   "company_name": "Example GmbH",
#   "company_address": "Musterstraße 1, 10115 Berlin",
#   "cached": false
# }