Send SMS with C# and the SMSFlow .NET SDK

Use the official SmsFlow .NET package to authenticate, send SMS and check balance from a backend application. Keep the Client Secret in environment variables, user secrets or a secret manager.

Install and prepare a controlled test

dotnet add package SmsFlow

Set SMSFLOW_CLIENT_ID and SMSFLOW_CLIENT_SECRET in your local/backend environment. Do not put real values in source, client-side code, screenshots or public issues. Use a supported .NET project with top-level statements; the current .NET quickstart documents package compatibility.

Send using the SDK

using SmsFlow;

var client = new SmsFlowClient(new SmsFlowClientOptions
{
    ClientId = Environment.GetEnvironmentVariable("SMSFLOW_CLIENT_ID")!,
    ClientSecret = Environment.GetEnvironmentVariable("SMSFLOW_CLIENT_SECRET")!,
    Timeout = TimeSpan.FromSeconds(30)
});

var response = await client.SendSmsAsync(new SendSmsRequest
{
    CampaignName = "Website synthetic example",
    Messages = new[]
    {
        new SmsMessage
        {
            Destination = "27000000000",
            Content = "Your demo appointment is confirmed for 10:00."
        }
    }
});
Console.WriteLine(response.SendResponse?.EventId);

The destination is synthetic. Replace it only with a recipient authorised for your controlled test. A real send consumes credits. The library handles the documented authentication flow; receiving an event/reference does not establish handset delivery.

Check balance and handle errors

var balance = await client.GetBalanceAsync();
Console.WriteLine(balance.Balance);

Validate your inputs and inspect errors using the API troubleshooting reference. Preserve useful non-sensitive correlation information. Avoid logging credentials or full customer message payloads. Investigate uncertain send outcomes before retrying; do not introduce an automatic replay loop around a whole campaign.

Use the published sources

NuGet package, SDK source and issues, version support and API overview. The public library covers authentication, sending and balance; discuss other operating requirements separately.

Check segment pricing before increasing your test volume. Java and other languages can use the raw HTTP examples.

Put the example into an application workflow

Keep the API credentials in your backend’s secret configuration.
Associate the returned event reference with the business event that triggered the message.
For an authentication or validation error, fix the cause before trying again. For an uncertain timeout, investigate the outcome before resending.

For 100 one-part test messages, the standard sending cost is R16 excluding VAT / R18.40 including VAT. Start with one authorised recipient, not the full list. Compare API capabilities and costs and the other supported libraries.

Sending SMS with C# using the SMSFlow .NET SDK