$url = 'https://www.newsletter2go.de/de/api/get/status';
    $data = [
      'key' => 'UNSER-API-KEY'
    ];

    //url-ify the data for the POST
    foreach($data as $key=>$value) { $data_string .= $key.'='.$value.'&'; }
    $data_string = rtrim($data_string,'&');

    //debug
    echo($data_string);

    //open connection
    $ch = curl_init();

    //set the url, number of POST vars, POST data
    curl_setopt($ch,CURLOPT_URL,$url);
    curl_setopt($ch,CURLOPT_POST,count($data));
    curl_setopt($ch,CURLOPT_POSTFIELDS,$data_string);

    //execute post
    $result = curl_exec($ch);

    //debug
    print $result;

    //close curl
    curl_close($ch);