"message" : "Your request body is not valid JSON."

why i get this response when i try to request this API : https://apidocs.tokeet.com/ i have valid ID and TOCKEN

$data=array(
        'name'     =>      'osama shaheen',
        'due'      =>      '500000',
        'list'     =>      'none',
    );
    $data=json_encode($data);
    //dd($data);
    $curl = curl_init();
    curl_setopt_array($curl, array(
        CURLOPT_URL => "http://capi.tokeet.com/v1/task?account={{ID}}",
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_ENCODING => "",
        CURLOPT_MAXREDIRS => 10,
        CURLOPT_TIMEOUT => 30,
        CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
        CURLOPT_CUSTOMREQUEST => "POST",
        CURLOPT_FOLLOWLOCATION => true,
        CURLOPT_SSL_VERIFYPEER  => false,
        CURLOPT_HTTPHEADER => array(
            "Authorization: {{TOCKEN}}",
            "Content-Type: application/json"
        ),
        CURLOPT_POSTFIELDS  =>$data,
        ));

    $response = curl_exec($curl);
    $err = curl_error($curl);

    curl_close($curl);

    if ($err) {
        echo "cURL Error #:" . $err;
    } else {
        echo $response;
    }