Invalid Grant Type oAuth 2.0 Auth Token

I have been struggling with the following code for some time. I get the following eror: {"error":"invalid_request","error_description":"invalid grant type"}.

Some more documentation on the API that I am working on is available here:

<?php

$curl = curl_init();

curl_setopt_array($curl, array(
  CURLOPT_URL => "https://id.shoeboxed.com/oauth/token",
   CURLOPT_RETURNTRANSFER => true,
  CURLOPT_SSL_VERIFYPEER => false, 
  CURLOPT_POST => 1,  
  CURLOPT_POSTFIELDS => "{\"code\": \"['code']\",\"grant_type\":\"authorization_code\",\"redirect_uri\": \"http://website.com/foursquare2.php\",\"client_id\": \"f8de67be8dc84e449203fcdd4XXXXXXX\",\"client_secret\": \"HS5ZeIVsKW0/qqiO9/XcdeWqnF8vtzQrpY8gcdrxg0BXNZXXXXXXX\"}",
  CURLOPT_HTTPHEADER => array(
    "application/x-www-form-urlencoded" 
  )
));


/*
//Another Attempt at it is below
curl -d code=['code'] \
    -d grant_type=authorization_code \
    --data-urlencode redirect_uri='http://website.com/foursquare2.php' \
    -u f8de67be8dc84e449203fcdd44abad5a:HS5ZXXXXXXX/qqiO9/XcdeWqnF8vtzQrpY8gcdrxg0BXNXXXXXXX \
    -XPOST https://id.shoeboxed.com/oauth/token 
*/


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

curl_close($curl);

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

?>

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