redirect_uri mismatch with unknown cause php

I was using my php curl to request a token from the api. I set up my parameter array correctly. However, I get this error in return :{"error_description": "redirect_uri mismatch", "error": "invalid_grant"}400

This was my implementation:

$dropbox_url = "https://api.dropboxapi.com/oauth2/token";
$timeout = 40;
$app_key = key;
$app_secret = secret;
try {
$d1curl = curl_init();
$http_headers = array(
	"Authorization: Basic " . base64_encode($app_key . ":" . $app_secret),
	"Content-Type: application/x-www-form-urlencoded"
	);
$parameters = array(
	'code' => $code,
	'grant_type' => 'authorization_code',
	'redirect_uri' => url	
);
curl_setopt($d1curl, CURLOPT_URL, $dropbox_url);
curl_setopt($d1curl, CURLOPT_TIMEOUT, $timeout);
curl_setopt($d1curl, CURLOPT_HTTPHEADER, $http_headers);
curl_setopt($d1curl, CURLOPT_POST, true);
curl_setopt($d1curl, CURLOPT_POSTFIELDS, http_build_query($parameters));
curl_setopt($d1curl, CURLOPT_RETURNTRANSFER, true);
$_SESSION['code'] = $_GET['code'];
$_SESSION['token'] = curl_exec($d1curl);
$http_request = curl_getinfo($d1curl, CURLINFO_HTTP_CODE);
echo $_SESSION['token'];
echo $http_request;
curl_close($d1curl);
}
catch(Exception $e) {
	echo curl_error($d1curl);
	curl_close($d1curl);
}

 I copied and pasted it right out of my api console to double check the url itself.