Fatal error how to get correct answer tried many solutions

Fatal error: Uncaught Error: Call to undefined function VALUES() in C:\xampp\htdocs\signuptest\Signup.php:32 Stack trace: #0 {main} thrown in C:\xampp\htdocs\signuptest\Signup.php on line 32

<?php
session_start();
$_SESSION['message']='';

$mysqli = new mysqli('localhost','root', '' , 'signuptest');

if ($_SERVER['REQUEST_METHOD'] == 'POST')  {
    
    //two passwords are equal to each other
    
    if($_POST['password'] == $_POST['confirmpassword']) {
        
        $firstname = $mysqli->real_escape_string($_POST['firstname']);
        $lastname = $mysqli->real_escape_string($_POST['lastname']);
        $email = $mysqli->real_escape_string($_POST['email']);
        $phonenumber = $mysqli->real_escape_string($_POST['phonenumber']);
        $password = md5($_POST['password']); //md5 hash password for security
        $avatar_path = $mysqli -> real_escape_string('image/'.$_FILES['avatar']['name']);
        
        //make sure file type
        
        if (preg_match("!image!", $_FILES['avatar']['type'])) {
           
            //copy image to images/ folder
            
            if(copy($_FILES['avatar']['tmp_name'], $avatar_path)){
                
                $_SESSION['firstname']= $firstname;
                $_SESSION['avatar']= $avatar_path;
                
                $sql = "INSERT INTO users(firstname,lastname,email,phonenumber,password,avatar)"
                .VALUES ('$firstname','$lastname','$email','$phonenumber','$password','$avatar_path');
               
                
                // if the qurey is succesful, redirect to welocme.php page, done!
                
                if ($mysqli -> query($sql) === true) {
                    $_SESSION['message'] = 'Registration Succesful! Added $username to the database!';
                    header("location: welcome.php");
                }
                
                else{
                    $_SESSION['message'] = 'User could not be added to the database';
                  
                }
            }
            
            else{
                $_SESSION['message'] = "File upload failed!";
            }
        }
        else{
            $_SESSION['message'] = "Please only upload JPG files";
        }
    }
    
    else{
        $_SESSION['message'] = "Two Passwords Doesn't match";
    }
}