title: Content-Language header throws Misused header name error when calling Ebay API
body: <p>When I make a PUT request to CreateOrReplaceInventoryItem using the Ebay API, I get this error:</p>
  
  <blockquote>
    <p>Misused header name. Make sure request headers are used with
    HttpRequestMessage, response headers with HttpResponseMessage, and
    content headers with HttpContent objects.</p>
  </blockquote>
  
  <p>The below code throws the error.</p>
  
  <pre><code>using (var client = new HttpClient())
  {
      var baseUri = new Uri(string.Format("https://api.sandbox.ebay.com/sell/inventory/v1/inventory_item/{0}", SKU));
      client.DefaultRequestHeaders.Add("Authorization", string.Format("Bearer {0}", token));
      client.DefaultRequestHeaders.Add("Content-Language", "en-US");
  
      var payload = JsonConvert.SerializeObject(product);
      var content = new StringContent(payload, Encoding.UTF8, "application/json");
  
      var response = client.PutAsync(baseUri, content).Result;
      return response.Content.ReadAsStringAsync().Result;
  }
  </code></pre>
  
  <p>If I remove the line:</p>
  
  <pre><code>client.DefaultRequestHeaders.Add("Content-Language", "en-US");
  </code></pre>
  
  <p>Then I get a returned error object:</p>
  
  <pre><code>errors":[{"errorId":25709,"domain":"API_INVENTORY","subdomain":"Selling","category":"REQUEST","message":"Invalid value for header Content-Language."}]} 
  </code></pre>
  
  <p>What am I doing wrong?  Is there another way to set Content-Language that I'm unaware of?</p>