Posting data with curl to secure page - php

Question

I'm trying to post pin and number of giftcard to BarnesAndNoble site to get the available balance. (we are a company buying gift cards from people, and we need to verify the balance)
https://cart2.barnesandnoble.com/gc/gc_ViewBalance.asp
The weird thing is that, the content returned is the original page (not the resulted page where it should say the pin&number entered are invalid, or should return an amount)
I wonder why it doesn't work, the code is pretty straight forward
$ch = curl_init();
$formUrl = 'https://cart2.barnesandnoble.com/gc/gc_ViewBalance.asp ';
$ckfile = __DIR__.'\cookie.txt';
curl_setopt($ch, CURLOPT_URL, $formUrl);
curl_setopt($ch, CURLOPT_REFERER, $formUrl);
curl_setopt($ch, CURLOPT_USERAGENT, $_SERVER['HTTP_USER_AGENT']);
$urldata = parse_url($formUrl);
$headers = array("Host: ".$urldata['host']);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
// tried this as well
//curl_setopt ($ch, CURLOPT_CAINFO, dirname(__FILE__)."/GTECyberTrustGlobalRoot.crt");
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
//curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, true);
//curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); // return content as a string
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, false);
curl_setopt($ch, CURLOPT_COOKIESESSION, true);
curl_setopt($ch, CURLOPT_COOKIEJAR, $ckfile);
curl_setopt($ch, CURLOPT_COOKIEFILE, $ckfile);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $post);
$content = curl_exec($ch);;

Answer 1

To answer my own question:
PHP curl resets content-length if CURLOPT_POST is set with curl_setopt_array?
Long answer: read the above link
Short answer: pass the query string into CURLOPT_POSTFIELDS instead of an array (I used array in the above $post)