Chatbot Facebook using PHP

chatbot.php

<?php
    $token = '';
    if(isset($_REQUEST['hub_challenge'])){
        $challenge = $_REQUEST['hub_challenge'];
        $token = $_REQUEST['hub_verify_token'];
    }
    
    if($token === "ar"){
        echo $challenge;
    }  


    // $input = file_get_contents('php://input');

    // var_dump($input);

    $input_f = (array)json_decode(file_get_contents('php://input'), true);

    // echo $input_f;
    // echo($input_f['entry']);
    $userid = $input_f['entry'][0]['messaging'][0]['sender']['id'];
    $message = $input_f['entry'][0]['messaging'][0]['message']['text'];
    $echo = false;

    if(isset($input_f['entry'][0]['messaging'][0]['message']['is_echo'])){
        $echo = true;
    }

    $sends = '';
    if($message == "hello"){
        $sends = "Hello, How i help you!";
    } 
    elseif ($message == "Need to buy"){
        $sends = "What you wanted to buy!";
    }
    elseif ($message == "Game"){
        $sends = "Okieee";
    }
    elseif ($message == "AAAA"){
        $sends = "What you actully Mean!!! ";
    }
    elseif ($message == "funny"){
        $sends = "I am not FB";
    }
    elseif ($message == "work"){
        $sends = "Ya sure";
    }
    else {
        $sends = 'Sorry Cant Understand you';
    }


    if(!$echo){
        echo $userid . " and " . $message. "and send " . $sends;

        $acc = "EAAgr7wgbbAQBANTjSx5mBLdBgIhmD24ZCSbaJCYZCF2QjQ6yUAxXmNeYOQVXLfcApQexal10dsxZCDHW5Hv0yljfoeUZBkHePIYOaZCCkJVlUC0F4XRWE36tZAw2YWGIVpaGhQZDZD";
        $url = "https://graph.facebook.com/v2.6/me/messages?access_token=$acc";

        
        $jsonss="{
            'recipient':{'id': $userid },
            'message':{'text': '". $sends."'  }
        }";
        echo $jsonss;
        $ch = curl_init($url);

        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $jsonss);
        curl_setopt($ch, CURLOPT_HTTPHEADER, ['Content-Type: application/json']);

        if(!empty($input_f['entry'][0]['messaging'][0]['message']) ){
            curl_exec($ch);
        }
    } else {
        echo 'Echo Found';
    }



?>