The incoming message has an unexpected message format 'Raw'. The expected message formats for the operation are 'Xml'

Question

I am doing a post request to an API, When I use postman, everything works fine as expected and data is returned. When I use Guzzler, cURL or file_get_contents(), I get this long error that the incoming message has an unexpected format 'Raw'.

My search on the net suggested that I use Content-Type: application/JSON but that doesn't solve it in my case. This is my code:

$user =auth()->user();
        
        $postRequest = array(
            'userId' => $user->id,
            'username' => $user->username,
            'currency'=> 'TRY',
            'nick'=>$user->username
        );
         $tvbetURL ="https://somewebsite.com/set_user_data";
        

        $headers = [
            'token' => '=EDMwU2N2MjM0kDNiVjYiFskljbgkjgerHUIHIOFG',
            'Content-Type' => 'application/json ',
            
            
        ];
        
        $client = new GuzzleClient([
            'headers' => $headers
        ]);
        
       
        
        
        $r = $client->request('POST', $tvbetURL, [
            'form_params' =>$postRequest
        ]);
        $response = $r->getBody()->getContents();
        dd($response);

THE ERROR:

[2020-08-28 07:05:51] production.ERROR: Server error: POST https://somewebsite.com/set_user_data resulted in a 500 Internal Server Error response: The incoming message has an unexpected message format 'Raw'. The expected message formats for the operation are 'Xml', ' (truncated...) {"userId":1,"exception":"[object] (GuzzleHttp\Exception\ServerException(code: 500): Server error: POST https://somewebsite.com/set_user_data resulted in a 500 Internal Server Error response: The incoming message has an unexpected message format 'Raw'. The expected message formats for the operation are 'Xml', ' (truncated...) at /opt/lampp/htdocs/projects/freelance/git/vendor/guzzlehttp/guzzle/src/Exception/RequestException.php:113) [stacktrace] Thank you i advance.