C# Quickstart

The one-line version, for reference:

curl -X POST "https://api.labelzoom.com/api/v2/convert/zpl/to/pdf" -H "Authorization: Bearer YOUR_API_KEY" -H "Content-Type: text/plain" -d '^XA^FO50,50^ADN,36,20^FDLabelZoom^FS^XZ' --output label.pdf

The same conversion with HttpClient (.NET 6+):

using System.Net.Http.Headers;

var zpl = "^XA^FO50,50^ADN,36,20^FDLabelZoom^FS^XZ";
var apiKey = Environment.GetEnvironmentVariable("LABELZOOM_API_KEY");

using var client = new HttpClient();
// The API key is optional — omit the Authorization header if it isn't set.
if (!string.IsNullOrEmpty(apiKey))
{
    client.DefaultRequestHeaders.Authorization =
        new AuthenticationHeaderValue("Bearer", apiKey);
}

var content = new StringContent(zpl, System.Text.Encoding.UTF8, "text/plain");
var response = await client.PostAsync(
    "https://api.labelzoom.com/api/v2/convert/zpl/to/pdf?label.width=4&label.height=6&dpi=203",
    content);

response.EnsureSuccessStatusCode();
await File.WriteAllBytesAsync("label.pdf", await response.Content.ReadAsByteArrayAsync());
Console.WriteLine("Wrote label.pdf");

Converting a PDF to ZPL

var pdfBytes = await File.ReadAllBytesAsync("shipping-label.pdf");
var pdfContent = new ByteArrayContent(pdfBytes);
pdfContent.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");

var response = await client.PostAsync(
    "https://api.labelzoom.com/api/v2/convert/pdf/to/zpl", pdfContent);
response.EnsureSuccessStatusCode();
var zpl = await response.Content.ReadAsStringAsync();

In ASP.NET Core, register the client with IHttpClientFactory instead of newing it per request. All endpoint patterns and parameters: quickstart · Swagger reference.