$username = 'XXXXXXXXXXXXXXXX';
  $password = 'XXxxxxxXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX';

  $curl = curl_init();

  curl_setopt($curl, CURLOPT_POST, 1);
  curl_setopt($curl, CURLOPT_URL, "https://api.neteller.com/v1/oauth2/token?grant_type=client_credentials");
  curl_setopt($curl, CURLOPT_USERPWD, "$username:$password");
  curl_setopt($curl, CURLOPT_HTTPHEADER, array("Content-Type:application/json", "Cache-Control:no-cache"));
  curl_setopt($curl, CURLOPT_POSTFIELDS, array("scope"=>"default"));
  curl_setopt($curl, CURLOPT_FOLLOWLOCATION, true);
  curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
  curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, false);
  curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);

  $serverOutput = curl_exec($curl);
  $info = curl_getinfo($curl);

  echo $serverOutput; // null response