Autodesk Forge token reauthorization command doesn't recognize parameters - autodesk-forge

Question

I am using Laravel / PHP on the back end to communicate with the Forge system. To establish an initial token, I am using the guzzle tool kit. This works fine.
// Get environment variables
$FusionID = getenv('THISID');
$FusionSecret = getenv('THISSECRET');
// Make call to get token with authorization code, client id, and secret
$client = new Client(); //GuzzleHttp\Client
$response = $client->request('POST', 'https://developer.api.autodesk.com/authentication/v1/gettoken', [
'form_params' => [
'grant_type' => 'authorization_code',
'code' => $authCode,
'client_id' => $FusionID,
'client_secret' => $FusionSecret,
'redirect_uri' => 'https://www.example.com/redirect',
'scope' => array('data'=>'create', 'data'=>'read')
]
]);
$body = $response->getBody();
$obj = json_decode($body);
For the numerous other commands, the guzzle protocol seems to have issues so I have been using the straight curl commands. However, I can't seem to get either to work for the refresh token.
I have verified that the variables below have the proper data, but I get the error that
"developerMessage":"The required parameter(s) client_id,client_secret,grant_type not present in the request","userMessage":"","errorCode":"AUTH-008",
I am not sure what to do. Both the guzzle method and the curl method do not seem to be working for me.
$thumbData = '{"client_id":"'.$FusionID.'",
"client_secret":"'.$FusionSecret.'",
"grant_type":"refresh_token",
"refresh_token":"'.$userInfo->refresh_token.'"}';
$url = 'https://developer.api.autodesk.com/authentication/v1/refreshtoken';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $thumbData );
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Content-Type: application/x-www-form-urlencoded'
));
$response = curl_exec ($ch);
$err = curl_error($ch);
curl_close ($ch);

Answer 1

The way you post x-www-form-urlencoded data with Guzzle looks fine so that leaves the question to be whether your Guzzle version is 6+ otherwise use body instead of form_params as your payload option.
With cURL you request body should be delimited by & in x-www-form-urlencoded format like below instead of `json:
curl_setopt($ch, CURLOPT_POSTFIELDS,
"client_id=sb233&client_secret=2333&...");