Error code 410 when polling Skyscanner flight live prices - php

Question

I am polling live prices from the Skyscanner API. Although I receive the session_key and although I am immediately polling the results I am getting a 410 (Gone) response header with an empty body. It used to work fine from my localhost environment but not on my live server anymore.
Has anybody experienced this before and can maybe give me a hint what the issue could be?
$url_api = "http://partners.api.skyscanner.net/apiservices/pricing/v1.0/";
$api_key = "XXX"; // Not shown here
$data = array('apiKey' => $api_key, 'country' => 'DE', 'currency' => 'EUR',
'locale' => 'de-DE', 'originplace' => 'HAM', 'destinationplace' => 'AMS', 'cabinclass' => 'economy', 'outbounddate' => '2017-01-27',
'inbounddate' => '2017-01-30' , 'locationschema' => 'Iata', 'groupPricing' => true);
$httpdata = http_build_query($data);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url_api);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $httpdata);
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/x-www-form-urlencoded', 'Accept: application/json'));
curl_setopt($ch, CURLOPT_VERBOSE, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_ENCODING, 'gzip');
curl_setopt($ch, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4 );
$response = curl_exec($ch);
curl_close($ch);
$headers = get_headers_from_curl_response($response);
$url = $headers['Location']."?apiKey=".$api_key."&stops=0";
echo $url;
return;