title: HttpClient - This instance has already started
body: <p>I'm getting this exception using http client in my api.</p>
  
  <blockquote>
    <p>An unhandled exception has occurred while executing the request.
    System.InvalidOperationException: This instance has already started one or more requests. Properties can only be modified before sending the first request.</p>
  </blockquote>
  
  <p>and I injected my service as </p>
  
  <pre><code>services.AddSingleton&lt;HttpClient&gt;()
  </code></pre>
  
  <p>I thought singleton was my best <a href="https://docs.microsoft.com/en-us/aspnet/web-api/overview/advanced/calling-a-web-api-from-a-net-client" rel="noreferrer">bet</a>. what could be my problem?</p>
  
  <p><strong>edit:</strong> my usage</p>
  
  <pre><code>class ApiClient
  {
     private readonly HttpClient _client;
     public ApiClient(HttpClient client)
     {
        _client = client;
     }
  
     public async Task&lt;HttpResponseMessage&gt; GetAsync(string uri)
     {
       _client.BaseAddress = new Uri("http://localhost:5001/");
       _client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json");
       var response = await _client.GetAsync(uri);
  
       return response;
     }
   }
  </code></pre>