title: Sendbird/Guzzle returns "The request body is an invalid JSON"
body: <p>I got an error message when trying to send a request to SendBird API using Guzzle.</p>
  
  <p>Error message</p>
  
  <pre><code>"message": "Client error: `POST https://api.sendbird.com/v3/group_channels` resulted in a `400 BAD REQUEST` response:\n{\"message\":\"Not valid JSON body.\",\"code\":400403,\"error\":true}\n",
      "exception": "GuzzleHttp\\Exception\\ClientException",
  </code></pre>
  
  <p>My code</p>
  
  <pre><code>$client = new Client([
                          'headers' =&gt; [
                              'Accept' =&gt; 'application/json',
                              'Authorization' =&gt; 'Bearer XXXXX',
                              'Content-Type' =&gt; 'application/json',
                          ],
                      ]); 
                      $response = $client-&gt;post('https://api.sendbird.com/v3/group_channels', [
                          'form_params' =&gt; [
                              'user_ids' =&gt; [$user_id_1,$user_id_2],
                              'operator_ids' =&gt; [$user_id_1,$user_id_2]
                          ]
                      ]);
  </code></pre>