C#: Parse DLR from an Android SMS Gateway API

C# parse DLR on an android sms gateway api is mapping delivery state after the SIM transmitted — or failed to. Product: delivery reports. Samples: C# REST examples. Docs: Developer Center.

You bring the Android and airtime. We meter devices and volume.

Accepted is not delivered

Send returns a batch with Pending:

{
  "campaignId": 17,
  "accepted": 1,
  "scheduledAt": null,
  "messages": [
    {
      "id": 41822,
      "number": "+14155552671",
      "text": "Your verification code is 481920",
      "type": "sms",
      "status": "Pending",
      "campaignId": 17,
      "deviceId": 3
    }
  ]
}

If you mark the user “notified” on 202, you will debug ghost OTPs that never left the dock.

How to parse DLR in C#

1. Persist messages[].id.
2. GET that id or wait for webhook.
3. Map status / deliveredAt.
4. Do not treat DLR as login success.

GET /messages/{id}

curl -X GET "https://app.sms-gateway.app/api/v1/messages/41822" \
  -H "Authorization: Bearer $SMS_GATEWAY_API_KEY"

Confirm the GET body in docs. The sketch below assumes a message object — match OpenAPI, do not invent properties.

Status map

API overview. JsonDocument: System.Text.Json.

Prefer webhooks

{
  "id": "evt_01K2F8QW3N4RXB7M",
  "type": "message.delivered",
  "createdAt": "2026-08-12T14:04:09Z",
  "apiVersion": "2026-08-12",
  "data": {
    "message": {
      "id": 41823,
      "number": "+14155552671",
      "text": "Your verification code is 481920",
      "status": "Delivered",
      "campaignId": 17,
      "deviceId": 3,
      "metadata": { "orderId": "1234" },
      "sentAt": "2026-08-12T14:04:02Z",
      "deliveredAt": "2026-08-12T14:04:09Z"
    }
  }
}

HMAC + event-id unique. Server webhook · /webhook.

Mapper sketch

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

public sealed record GatewayMessage(int Id, string Status, string Number);

public static async Task<GatewayMessage?> GetDlrAsync(HttpClient http, string apiKey, int id)
{
    http.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", apiKey);
    using var res = await http.GetAsync(
quot;https://app.sms-gateway.app/api/v1/messages/{id}");
    res.EnsureSuccessStatusCode();
    using var doc = JsonDocument.Parse(await res.Content.ReadAsStringAsync());
    var root = doc.RootElement;
    // Confirm the live JSON shape in Developer Center — this is a mapper sketch.
    var status = root.GetProperty("status").GetString() ?? "Unknown";
    var number = root.TryGetProperty("number", out var n) ? n.GetString() ?? "" : "";
    return new GatewayMessage(id, status, number);
}

OTP send path: ASP.NET OTP.

DLR is not a refund

Failed after the SIM fired still cost airtime. Free: 300 SMS lifetime. Developer: 25,000/year. Starter/Pro/Business uncap platform volume, devices 2/5/15. Pause on Free/Developer at allowance. No unlimited carrier SMS. Pricing.

Checklist

• Message id stored before you return to the user.
• Webhook HMAC in production; poll only as fallback.
• Status switch exhaustive + default log.
• No auto-resend loop on Failed.

Next steps

Send one staff SMS, GET the id, then fire a webhook into a test controller. Downloads.