Error 107 invalid date with parse REST API - rest

Question

I'm trying to authenticate a facebook user using parse REST API, but after sending the json via CURL, it gives me the following error message:
{
"code":107,
"error":"Invalid date"
}
The documentation states the following about the expiration_date format in the json that must be sent:
{
"facebook": {
"id": "user's Facebook id number as a string",
"access_token": "an authorized Facebook access token for the user",
"expiration_date": "token expiration date of the format: yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
}
}
Here is the code I'm using for setting the date to the ISO8601 format that I think parse requires:
$session = $helper->getSessionFromRedirect();
$request = new FacebookRequest( $session, 'GET', '/me' );
$response = $request->execute();
$graphObject = $response->getGraphObject();
$token = $session->getToken();
$info = $session->getSessionInfo();
$expiresAt = $info->getExpiresAt();
$expiresAtFormatted = $expiresAt->format(\DateTime::ISO8601);
$facebook = array(
'authData' => array(
'facebook' => array(
'id' => $id,
'access_token' => $token,
'expiration_date' => $expiresAtFormatted
)
)
);
$facebookJson = json_encode($facebook);
And here is the var_dump of the $expiresAtFormatted variable:
string(24) "2015-02-23T18:17:59+0000"