Symofny - curl return invalid request : I am using cashflows documentation with specified url to try to return test request but dump() returns this error..

> "V|99E5BB5DF59|000|V226|Invalid request\n"

or

> The controller must return a response (V|99E5BB5DFC6|000|V226|Invalid request
given).

My code..


     // jSON URL which should be requested
        $json_url = 'https://secure.cashflows.com/gateway/remote';

        $username = '5949138';  // authentication
        $password = 'Ad368w9XYw';  // authentication

        // jSON String for request
        $json_string = [
            'amount' => 'amount',
            'currency' => 'currency',
        ];

        // Initializing curl
        $ch = curl_init( $json_url );

        // Configuring curl options
        $options = array(
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_USERPWD	=> $username . ':' . $password,  // authentication
        CURLOPT_HTTPHEADER => array('Content-type: application/json') ,
        CURLOPT_POSTFIELDS => $json_string,
    );

        // Setting curl options
        curl_setopt($ch, CURLOPT_ENCODING, 'UTF-8');
        curl_setopt_array( $ch, $options );

        // Getting results
        $result = curl_exec($ch); // Getting jSON result string
        
        return $result;

I can't figure out what is causing the problem.