CURLOPT_POST must be left unset if you want the Content-Type header set to "multipart/form-data" (e.g., when CURLOPT_POSTFIELDS is an array). If you set CURLOPT_POSTFIELDS to an array and have CURLOPT_POST set to TRUE, Content-Length will be -1 and most sane servers will reject the request. If you set CURLOPT_POSTFIELDS to an array and have CURLOPT_POST set to FALSE, cURL will send a GET request.