Warning: Attempt to read property “username” on null in C:UsershpDesktopxampphtdocs19Aprilmain.php on line 33

I am trying to fetch data from the database and getting the error as:

Warning: Attempt to read property “username” on null in C:UsershpDesktopxampphtdocs19Aprilmain.php on line 33

Please suggest/guide me through the solution

My main.php file

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <h3>Search Meetings</h3>
    <form action="" method="POST">
        <!-- <label>Enter Your Name:</label><br /> -->
        <input type="text" name="username" placeholder="Your Name" required/>
        <br /><br />
        <button type="submit" name="submit">Search</button>
    </form>  
</body>
</html>

<?php

if(isset($_POST['username']) && $_POST['username']!=""){
    $username = $_POST['username'];
    $url = "http://localhost/19April/api/".$username;

    $client = curl_init($url);
    curl_setopt($client,CURLOPT_RETURNTRANSFER,true);
    $response = curl_exec($client);
    
    $result = json_decode($response);
    
    // echo "<table>";
    echo "<tr><td>User Name:</td><td>$result->username</td></tr>";
    // echo $result->$username;
    // echo "<tr><td>Age:</td><td>$result->age</td></tr>";
    // echo "<tr><td>Email-Id:</td><td>$result->email</td></tr>";
    // echo "</table>";
}
?>

My api.php file

<?php
header("Content-Type:application/json");

if (isset($_GET['username']) && $_GET['username']!="") {
    include('db.php');
    $username = $_GET['username'];
    $result = mysqli_query($con,"SELECT * FROM `transactions` WHERE username=$username");

    if(mysqli_num_rows($result)>0){
        $row = mysqli_fetch_array($result);
        $username = $row['username'];
        $age = $row['age'];
        $email = $row['email'];
        response($username, $username, $age,$email);
        mysqli_close($con);
    }else{
        response(NULL, NULL, 200,"No Record Found");
    }
}else{
    response(NULL, NULL, 400,"Invalid Request");
}

function response($username,$age,$email){
    $response['username'] = $username;
    $response['age'] = $age;
    $response['email'] = $email;
    
    $json_response = json_encode($response);
    echo $json_response;
}
?>