Facebook messenger bot using PHP - Postback example? -

i developing fb messenger bot using php, have query regarding button click event, how trigger & call new card/text. can please explain example button postback using php?

is mean?

https://github.com/pimax/fb-messenger-php-example/blob/master/index.php

$data = json_decode(file_get_contents("php://input"), true, 512, json_bigint_as_string);  if (!empty($data['entry'][0]['messaging'])) {           foreach ($data['entry'][0]['messaging'] $message) {           $command = "";          // when bot receive message user         if (!empty($message['message'])) {              $command = $message['message']['text'];                    }          // when bot receive button click user          else if (!empty($message['postback'])) {              $command = $message['postback']['payload'];         }     } }    // handle command switch ($command) {     // when bot receive "text"     case 'text':         $bot->send(new message($message['sender']['id'], 'this simple text message.'));         break;     // when bot receive "image"     case 'image':         $bot->send(new imagemessage($message['sender']['id'], 'https://developers.facebook.com/images/devsite/fb4d_logo-2x.png'));         break;     // when bot receive "image"     case 'local image':         $bot->send(new imagemessage($message['sender']['id'], dirname(__file__).'/fb4d_logo-2x.png'));         break;     // when bot receive "profile"     case 'profile':         $user = $bot->userprofile($message['sender']['id']);         $bot->send(new structuredmessage($message['sender']['id'],             structuredmessage::type_generic,             [                 'elements' => [                     new messageelement($user->getfirstname()." ".$user->getlastname(), " ", $user->getpicture())                 ]             ]         ));         break;     // when bot receive "button"     case 'button':       $bot->send(new structuredmessage($message['sender']['id'],           structuredmessage::type_button,           [               'text' => 'choose category',               'buttons' => [                   new messagebutton(messagebutton::type_postback, 'first button'),                   new messagebutton(messagebutton::type_postback, 'second button'),                   new messagebutton(messagebutton::type_postback, 'third button')               ]           ]       ));     break;     // when bot receive "generic"     case 'generic':         $bot->send(new structuredmessage($message['sender']['id'],             structuredmessage::type_generic,             [                 'elements' => [                     new messageelement("first item", "item description", "", [                         new messagebutton(messagebutton::type_postback, 'first button'),                         new messagebutton(messagebutton::type_web, 'web link', 'http://facebook.com')                     ]),                     new messageelement("second item", "item description", "", [                         new messagebutton(messagebutton::type_postback, 'first button'),                         new messagebutton(messagebutton::type_postback, 'second button')                     ]),                     new messageelement("third item", "item description", "", [                         new messagebutton(messagebutton::type_postback, 'first button'),                         new messagebutton(messagebutton::type_postback, 'second button')                     ])                 ]             ]         ));      break;     // when bot receive "receipt"     case 'receipt':         $bot->send(new structuredmessage($message['sender']['id'],             structuredmessage::type_receipt,             [                 'recipient_name' => 'fox brown',                 'order_number' => rand(10000, 99999),                 'currency' => 'usd',                 'payment_method' => 'visa',                 'order_url' => 'http://facebook.com',                 'timestamp' => time(),                 'elements' => [                     new messagereceiptelement("first item", "item description", "", 1, 300, "usd"),                     new messagereceiptelement("second item", "item description", "", 2, 200, "usd"),                     new messagereceiptelement("third item", "item description", "", 3, 1800, "usd"),                 ],                 'address' => new address([                     'country' => 'us',                     'state' => 'ca',                     'postal_code' => 94025,                     'city' => 'menlo park',                     'street_1' => '1 hacker way',                     'street_2' => ''                 ]),                 'summary' => new summary([                     'subtotal' => 2300,                     'shipping_cost' => 150,                     'total_tax' => 50,                     'total_cost' => 2500,                 ]),                 'adjustments' => [                     new adjustment([                         'name' => 'new customer discount',                         'amount' => 20                     ]),                     new adjustment([                         'name' => '$10 off coupon',                         'amount' => 10                     ])                 ]             ]         ));     break;     case 'set menu':         $bot->setpersistentmenu([             new messagebutton(messagebutton::type_web, "first link", "http://yandex.ru"),             new messagebutton(messagebutton::type_web, "second link", "http://google.ru")         ]);     break;     case 'delete menu':         $bot->deletepersistentmenu();     break;     // other message received     default:         $bot->send(new message($message['sender']['id'], 'sorry. don’t understand you.')); }