No problem. I think both URLs are valid, but I use the ipnpb one. Kinda going off topic now, so might be better to start a new thread if you need one. But if it's of any use, here's my cURL handling code. Don't know what problem you're having, but the main thing I'd say to watch out for is that you're doing type and value comparisons (===) and not just value comparisons (==, !).
if (( $hndl = curl_init( 'https://ipnpb.paypal.com/cgi-bin/webscr' )) === false ) throw new Exception( 'Error creating cURL handle' );
$send = 'cmd=_notify-validate';
foreach ( $_POST as $k => $v ) $send .= ( "&{$k}=" . urlencode( $v ));
if ( ! curl_setopt_array( $hndl, [CURLOPT_FAILONERROR => true, CURLOPT_RETURNTRANSFER => true, CURLOPT_POST => true, CURLOPT_POSTFIELDS => $send] ))
{
$errno = curl_errno( $hndl );
$errstr = curl_error( $hndl );
curl_close( $hndl );
throw new Exception( "Error setting cURL options: ({$errno}) '{$errstr}'" );
}
if (( $recv = curl_exec( $hndl )) === false )
{
$errno = curl_errno( $hndl );
$errstr = curl_error( $hndl );
$info = print_r( curl_getinfo( $hndl ), true );
curl_close( $hndl );
throw new Exception( "cURL response error: ({$errno}) '{$errstr}'\n{$info}\nsent: '{$send}'" );
}
curl_close( $hndl );
if ( $recv != 'VERIFIED' ) throw new Exception( "PayPal payment not verified: '{$recv}'\nsent: '{$send}'" );
