Strava API，无法让代币交换工作

我能够获得授权代码，但随后我无法使令牌交换正常工作。我得到的响应为空。

任何人都对此有任何见解，我已经搞砸了几个小时。

function tokenRequest($clientId, $clientSecret, $code){
$url =  'https://www.strava.com/oauth/token?';
$oauthFields = array(
    'client_id' => $clientId,
    'client_secret' => $clientSecret,
    'code' => $code);
$parameters = http_build_query($oauthFields);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url.$parameters);
curl_setopt($ch, CURLOPT_POST, count($oauthFields));
curl_setopt($ch, CURLOPT_POSTFIELDS, $parameters);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_USERAGENT, 'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.0.3705; .NET CLR 1.1.4322)');
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 1);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, TRUE);
$urlResponse = curl_exec($ch);
curl_close($ch);
return (json_decode($urlResponse));
}
if (isset($_GET['code'])){
   $code=$_GET['code'];
   echo "code is: " . $code . "</br>";
   $token = tokenRequest($clientId, $clientSecret, $code);
   var_dump($token);
}
else{echo "User denied access request";}