PayPal IPN Listener -- Sending Response w/ CURL

I'm trying t开发者_StackOverflow中文版o setup my PayPal IPN Listener with CURL. I'm receiving the POST data from Paypal just fine, but I'm stuck when sending my response back.

This is a test I'm trying to send back to Paypal, looking for the expected "VERIFIED" or "INVALID" response.

    $string = 'cmd=_notify-validate&test_ipn=1&payment_type=instant&payment_date=13%3A49%3A46+Dec+01%2C+2010+PST&payment_status=Completed&address_status=confirmed&payer_status=verified&first_name=John&last_name=Smith&payer_email=buyer%40paypalsandbox.com&payer_id=TESTBUYERID01&address_name=John+Smith&address_country=United+States&address_country_code=US&address_zip=95131&address_state=CA&address_city=San+Jose&address_street=123%2C+any+street&business=seller%40paypalsandbox.com&receiver_email=seller%40paypalsandbox.com&receiver_id=TESTSELLERID1&residence_country=US&item_name=something&item_number=AK-1234&quantity=1&shipping=3.04&tax=2.02&mc_currency=USD&mc_fee=0.44&mc_gross=12.34&mc_gross_1=9.34&txn_type=web_accept&txn_id=461212149&notify_version=2.1&custom=xyz123&charset=windows-1252&verify_sign=AHaXyf3zaDTb0y4MveMg3L5zjpqNAElZcXU6rvpq5jsGR30FGG6OehkN';

    $endpoint = 'https://www.sandbox.paypal.com/';

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $endpoint);
    curl_setopt($ch, CURLOPT_HEADER, TRUE);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
    curl_setopt($ch, CURLOPT_POST, TRUE);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $string);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, FALSE);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
    curl_setopt($ch, CURLOPT_TIMEOUT, 30);
    $result = curl_exec($ch);
    curl_close($ch);

    echo $result;

I'm using the Sandbox IPN Testing Simulator to send IPN signals to my listener. I'm sending my responses to https://www.sandbox.paypal.com/.

I get this response from Paypal no matter what data I send to it:

HTTP/1.1 301 Moved Permanently
Date: Wed, 01 Dec 2010 23:34:30 GMT
Server: Apache
Set-Cookie: c9MWDuvPtT9GIMyPc3jwol1VSlO=%7cPwtfdnvWZ1WVsa34w2F4FnUT4lXZCFSynqbMXEb4n-DLVEWN-dbmDX86YMRj6lgQyDfDGW%7cgeDqSysrRWP1DZZKq9pFf2j5ZBlu0nORtDS4-uXC_YGN8BtbwSBf1d6vq-77_078ySZeRG%7c; domain=.paypal.com; path=/
Set-Cookie: -1ILhdyICORs4hS4xTUr41S8iP0=cH14qDWDhwMs_KbBH2sE-6AG-wKvoQqYPWtsICHmeL1gU49_4McpLl14aXD3KVyvQsmhfiPzKd-Ekiwm; expires=Tue, 26-Nov-2030 23:34:31 GMT; domain=.paypal.com; path=/
Set-Cookie: cookie_check=yes; expires=Sat, 28-Nov-2020 23:34:31 GMT; domain=.paypal.com; path=/
Set-Cookie: Apache=10.191.196.11.135781291246470532; path=/; expires=Tue, 18-Oct-04 17:06:14 GMT
Location: https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_home&country_lang.x=true
Cneonction: close
Transfer-Encoding: chunked
Content-Type: text/plain; charset=ISO-8859-1

It makes me think I'm just plain posting to the wrong url, but that's the url I'm supposed to use.

Sandbox URL for Paypal is:

https://www.sandbox.paypal.com/cgi-bin/webscr