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---
title: Include file
description: include file
services: azure-communication-services
author: dbasantes
ms.service: azure-communication-services
ms.subservice: azure-communication-services
ms.date: 12/06/2024
ms.topic: include
ms.author: dbasantes
ms.custom:
- Include file
- sfi-ropc-blocked
---
Get started with Azure Communication Services SMS Opt-out API by applying the following C# sample code.
## Prerequisites
- An Azure account with an active subscription. [Create an account for free](https://azure.microsoft.com/pricing/purchase-options/azure-account?cid=msft_learn).
- The .NET Core SDK version must be higher than v6 for your operating system.
- An active Communication Services resource and connection string. See [Create a Communication Services resource](../../create-communication-resource.md).
- An SMS-enabled telephone number. See [Get a phone number](../../telephony/get-phone-number.md).
## Sample code to use Opt-Out API
This sample demonstrates how to use the Opt-Out Management API in C# to programmatically add, remove, or check opt-out entries.
```cs
using System.Globalization;
using System.Security.Cryptography;
using System.Text;
// Sample for Add action. Replace with Check or Remove as necessary.
async Task SendOptOutAdd(string acsResourceConnectionString, string payload)
{
const string ApiPrivatePreviewVersion = "2024-12-10-preview";
const string dateHeader = "x-ms-date";
string accesskey = GetConnectionStringPart(acsResourceConnectionString, "accesskey");
var endpointUri = new Uri(GetConnectionStringPart(acsResourceConnectionString, "endpoint"));
using var httpClient = new HttpClient();
httpClient.BaseAddress = endpointUri;
string method = "POST";
string baseAddress = httpClient.BaseAddress.ToString().TrimEnd('/');
var requestUri = new Uri($"{baseAddress}/sms/optouts:add?api-version={ApiPrivatePreviewVersion }", UriKind.RelativeOrAbsolute);
string hashedBody = ComputeSha256Hash(payload);
string utcNowString = DateTimeOffset.UtcNow.ToString("r", CultureInfo.InvariantCulture);
string stringToSign = $"{method}\n{requestUri.PathAndQuery}\n{utcNowString};{requestUri.Host};{hashedBody}";
string signature = ComputeHmacSha256Hash(accesskey, stringToSign);
string authHeader = $"HMAC-SHA256 SignedHeaders={dateHeader};host;x-ms-content-sha256&Signature={signature}";
using HttpRequestMessage request = new();
request.Headers.TryAddWithoutValidation(dateHeader, utcNowString);
request.Headers.TryAddWithoutValidation("x-ms-content-sha256", hashedBody);
request.Headers.TryAddWithoutValidation("Authorization", authHeader);
request.RequestUri = requestUri;
request.Method = new HttpMethod(method);
request.Content = new StringContent(payload, Encoding.UTF8, "application/json");
HttpResponseMessage response = await httpClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
Console.WriteLine(response.StatusCode);
Console.WriteLine(await response.Content.ReadAsStringAsync());
Console.WriteLine(response.Headers.ToString());
}
string ComputeSha256Hash(string rawData)
{
using SHA256 sha256Hash = SHA256.Create();
byte[] bytes = sha256Hash.ComputeHash(Encoding.UTF8.GetBytes(rawData));
return Convert.ToBase64String(bytes);
}
string ComputeHmacSha256Hash(string key, string rawData)
{
using HMACSHA256 hmacSha256 = new HMACSHA256(Convert.FromBase64String(key));
byte[] bytes = hmacSha256.ComputeHash(Encoding.ASCII.GetBytes(rawData));
return Convert.ToBase64String(bytes);
}
string GetConnectionStringPart(string acsResourceConnectionString, string key)
{
return acsResourceConnectionString.Split($"{key}=").Last().Split(';').First();
}
// Usage
const string ConnectionString = "endpoint=https://[CONTOSO].communication.azure.com/;accesskey=******";
var payload = System.Text.Json.JsonSerializer.Serialize(new
{
from = "+15551234567", //replace with your allowed sender number
recipients = new[] {
new { to = "+15550112233" } //replace with your recipient
},
});
await SendOptOutAdd(ConnectionString, payload);
```
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