ssl - PHP cURL POST returns Unsupported Media Type -

currently working integrating new e-commerce api (swish) having bit of struggle. i'm using php , curl in app perform test-connection merchant simulator. code looks follows:

$post = array(     "payeepaymentreference"=> "0123456789",     "callbackurl"=> "https://myssldomain.com",     "payeralias"=> "4671234768",     "payeealias"=> "1231181189",     "amount"=> "100",      "currency"=> "sek",     "message"=> "kingston usb flash drive 8 gb" );  $ch = curl_init();   curl_setopt($ch,curlopt_returntransfer, false);  curl_setopt($ch,curlopt_header, true); curl_setopt($ch,curlopt_url, 'https://mss.swicpc.bankgirot.se/swish-cpcapi/api/v1/paymentrequests/');  curl_setopt($ch,curlopt_ssl_verifypeer, true); curl_setopt($ch,curlopt_ssl_verifyhost, 0); curl_setopt($ch,curlopt_postfields, $post); curl_setopt($ch,curlopt_sslkey, 'sslkey.key'); curl_setopt($ch,curlopt_sslcert, 'sslcert.crt'); curl_setopt($ch, curlopt_cainfo, 'cainfo.crt');  $data = curl_exec($ch);  $error = curl_error($ch);  curl_close($ch);   var_dump($data); 

note: callback-url in post-array different. have valid, ssl-domain set there callback url.

the response when proceeding above code this:

http/1.1 415 unsupported media type server: apache-coyote/1.1 accept-ranges: bytes etag: w/"0-1448896356000" last-modified: mon, 30 nov 2015 15:12:36 gmt content-type: text/html content-length: 0 date: sun, 24 jan 2016 21:07:00 gmt 

the 3 parts of ssl-certificate can found @ swish's api site if download test-tool (guide testverktyg). can please tell me i'm doing wrong?

have tried adding

curl_setopt($ch, curlopt_httpheader, array('content-type: application/json'));