include_once 'vendor/autoload.php';

define( 'LS_BASEURL', 'https://localhost/limesurvey/'); // adjust this one to your actual LimeSurvey URL
define( 'LS_USER', 'rpcuser' );
define( 'LS_PASSWORD', 'mypassword' );

// the survey to process
$survey_id=99999;
try
{
// instantiate a new client
$myJSONRPCClient = new \org\jsonrpcphp\JsonRPCClient( LS_BASEURL.'/admin/remotecontrol' );

// receive session key
$sessionKey= $myJSONRPCClient->get_session_key( LS_USER, LS_PASSWORD );

// call method
$response = $myJSONRPCClient->mail_registered_participants( $sessionKey, $survey_id) ;

}
catch (Exception $e)
{
echo $e->getMessage() ;
}

// release the session key
$myJSONRPCClient->release_session_key( $sessionKey );