//Código JAVASCRIPT
function sendRequest(user) {
                FB.ui({
                    method: 'apprequests',
                    title: 'Concurso Hipoglos',
                    message: 'Invita a tus amigos a subir a tu bus de hipoglos y ganar fantasticos premios.',
                    data: '{"item_id":'+user+',"item_type":"plant"}'
                },
                function (response) {
                    if (response && response.request_ids) {

                        alert('Tus invitaciones han sido enviadas, tus amigos recibiran una notificacion para subir a tu bus. Recueda que estas participando cuando tengas 20 pasajeros en el bus.');

                    } else {

                        //Do something if they don't send it.

                    }
                });
            }        



//Rescatando datos desde php
if( isset($_REQUEST['request_ids']) ) {
                
                // Requesting an application token
                $token_url =    "https://graph.facebook.com/oauth/access_token?" .
                "client_id=" . $fbconfig['appid' ] .
                "&client_secret=" . $fbconfig['secret'] .
                "&grant_type=client_credentials";
                $app_token = file_get_contents($token_url);

                // You may have more than one request, so it's better to loop
                $requests = explode(',',$_REQUEST['request_ids']);  
                foreach($requests as $request_id) {
                    // Get the request details using Graph API
                    $request_content = json_decode(file_get_contents("https://graph.facebook.com/$request_id?$app_token"), TRUE);

                    // An example of how to get info from the previous call
                    $from_id = $request_content['from']['id'];
                    $to_id = $request_content['to']['id']; 

                    // An easier way to extract info from the data field
                    extract(json_decode($request_content['data'], TRUE));
                    // Now that we got the $item_id and the $item_type, process them
                    // Or if the recevier is not yet a member, encourage him to claims his item (install your application)! 
                    $redirect_from_app = $fbconfig['appUrl'] . "&app_data=" . $item_id;
                    $loginUrl = $facebook->getLoginUrl(array('scope' => 'email,publish_stream', 'redirect_uri' => $redirect_from_app));
                    // When all is done, delete the requests because Facebook will not do it for you!
                    //$deleted = file_get_contents("https://graph.facebook.com/$request_id?$app_token&method=delete"); // Should return true on success
                }
            }

Rescatamos los datos que pasamos por apprequest .

Request data from apprequest facebook api

url, javascript, data, api, facebook

PHP