Google Analytics请求会正确验证，但从CURL发送时会返回错误

Question

I'm sending the following request to Google Analytics:

http://www.google-analytics.com/collect?v=1&tid=UA-72579327-1&cid=61baecac-8f8c-4dce-bf07-a7efa24a4e47&t=transaction&ti=qcY6pvpWGmP9fHyi&tr=10.00&cd1=Acme Racing&cd2=http://www.domain.co.uk/affiliate/idevaffiliate.php/id=314&tid1=12044762460674420322&url=http://www.nitrotek.co.uk&cd3=A1&cd4=Upgrades&cd5=Acme-Tech &cd6={device}&cd7=&cd8=0&cd9=&cd10=&cd11=&cd12=Nitrotek DSA&cd13=g&cd14=50&cd15=1&cd16=85&cd17=12044762460674420322&cd18=&cd19=http://www.domain.co.uk&cd20=61baecac-8f8c-4dce-bf07-a7efa24a4e47&gclid=

When you go to Google's hit builder and validate the request, it comes out valid.

However, when I send the same request through CURL POST, I just get "400. That’s an error. Your client has issued a malformed or illegal request. That’s all we know.".

POST is the correct method for this request (though I have tried GET just in case) and the Content-Length header is the length of the sent data (string). Here is the code:

$curl = curl_init();
curl_setopt_array($curl, array(
    CURLOPT_RETURNTRANSFER => 1,
    CURLOPT_URL => $transaction_url,    //the same URL string given above
    CURLOPT_POST => 1,
    CURLOPT_USERAGENT => 'cURL Request'
));
curl_setopt($curl, CURLOPT_HTTPHEADER, array(
    'Content-Length: '.strlen($transaction_url)    //length of URL string
));
$trans_resp = curl_exec($curl);
var_dump($trans_resp);
curl_close($curl);