错误：SSL证书

Question

I use this API to send trade offers through Steam in PHP: https://github.com/halipso/php-steam-tradeoffers

But when I try to execute a function for send a trade offer, I receive this error:

Error: SSL certificate problem: unable to get local issuer certificate

I download cacert.pem, put it in my localhost folder and I edit the php.ini and nothing, the error still appear. I use WampServer.

The code that I use:

require_once 'classes/steam.class.php';

function SendTradeOffer()
{
    $steam = new SteamTrade();

    $steam->setup
    (
        'MTA3MTU3Mxxxxxx', // session id value here
        'sessionid=MTA3MTU3Mxxxxxx; steamLoginSecure=765611983077xxxxx%7c%7c23106D08073F26A02FE0B7EDC63F31xxxxxxxx' // cookieID
    );

    $invent = array
    (
        'contextId' => 2,  
        'appId' => 570,
        'tradableOnl' => true
    );

    $item = [];

    $itemThem = [['contextId' => 2,  
        'appId' => 730,
        'amount' => 1,
        'assetid' => "6576025395"]];


    $trade = [
        'partnerSteamId' => "76561xxxxxxxx",
        'itemsFromMe' => $item,
        'itemsFromThem' => $itemThem,
        'message' => 'gimme'];
}