How do I send an SMS with C#?

Make an HTTPS POST to https://api.bremlio.com/v1/messages with your API key in the X-Api-Key header and a JSON body of {"to", "message"}. The full C# example is above.

What do I need to start?

A Bremlio account and an API key (created in the dashboard). New accounts get 25 free credits, so you can run the example end to end before paying.

How much does it cost?

4.65p per SMS to a UK mobile, pay as you go, no monthly fee.

How do I check delivery?

The send response returns a message_id and status. Delivery status is then available in the dashboard and via the message-history API.

Home › Send SMS with C# (.NET)

Send SMS with C# (.NET)

Send an SMS to a UK mobile from C# with one HTTPS request to the Bremlio API. Real, runnable code — authentication, request, response and error handling — at 4.65p per message, pay as you go.

Get your API key free

1. Setup & authentication

Uses HttpClient from .NET. Read the API key from an environment variable. Create an API key in the Bremlio dashboard and authenticate by sending it in the X-Api-Key header. Numbers can be UK national (07…) or E.164 (+44…).

2. Send an SMS in C#

using System.Net.Http;
using System.Text;

using var http = new HttpClient();
var req = new HttpRequestMessage(HttpMethod.Post, "https://api.bremlio.com/v1/messages");
req.Headers.Add("X-Api-Key", Environment.GetEnvironmentVariable("BREMLIO_API_KEY"));
req.Content = new StringContent(
    "{\"to\":\"+447700900123\",\"message\":\"Your order has been confirmed.\"}",
    Encoding.UTF8, "application/json");
var resp = await http.SendAsync(req);
var body = await resp.Content.ReadAsStringAsync();
Console.WriteLine(resp.IsSuccessStatusCode ? $"accepted: {body}" : $"failed: {(int)resp.StatusCode} {body}");

3. The response

{
  "success": true,
  "message_id": "a1b2c3d4-…",
  "provider_message_id": "…",
  "status": "accepted",
  "credits_remaining": 24
}

4. Errors to handle

The API returns a JSON {"error": "..."} with an appropriate HTTP status. Common cases:

Status	Meaning
400	Invalid request — e.g. missing/!UK number, or empty/too-long message.
401	Invalid or missing API key.
402	Insufficient credits — top up to continue.
403	Account pending verification, recipient suppressed, or blocked by content policy.

5. Production tips

Keep the API key in an environment variable or secret store — never in source or client-side code.
Check status == "accepted" and store the message_id to reconcile delivery later.
Handle non-2xx responses and retry transient network errors with backoff (the send itself is a single request).
Validate/normalise numbers to +44 before sending to avoid 400s.

Frequently asked questions

How do I send an SMS with C#?: Make an HTTPS POST to https://api.bremlio.com/v1/messages with your API key in the X-Api-Key header and a JSON body of {"to", "message"}. The full C# example is above.
What do I need to start?: A Bremlio account and an API key (created in the dashboard). New accounts get 25 free credits, so you can run the example end to end before paying.
How much does it cost?: 4.65p per SMS to a UK mobile, pay as you go, no monthly fee.
How do I check delivery?: The send response returns a message_id and status. Delivery status is then available in the dashboard and via the message-history API.

Send your first SMS from C# today.