Image file upload not working properly

Question

I am working on a login system which is working pretty good already. Now I decided to add the feature that on registering, a user is able to upload an image to set as his profile picture. My code is mostly done but it doesn't seem to work and I can't figure out why. In the code below I made 2 if statements regarding the image, first I am trying to check if the image is an actual image file and after that I am copying the uploaded image to a folder in my directory, the path gets stated in $avatar when the picture is uploaded and the form gets submitted. When I upload a picture I manage to pass the first if statement but then it gives me the else statement that the file did not got uploaded. When I try to upload a different extension then the ones which are allowed I get no error at all and the script returns a blank screen, no user data gets posted on any of these occasions.

<?php
require_once('../connect.php');

if(isset($_POST) AND !empty($_POST)){
 
 $firstname = mysqli_real_escape_string($connection, $_POST['firstname']);
 $lastname = mysqli_real_escape_string($connection, $_POST['lastname']);
 $email = mysqli_real_escape_string($connection, $_POST['email']);
 $username = mysqli_real_escape_string($connection, $_POST['username']);
 $password = password_hash($_POST['password'], PASSWORD_DEFAULT);
 $avatar = mysqli_real_escape_string($connection, 'avatars/'.$_FILES['avatar']['name']);

 $extension = pathinfo($avatar, PATHINFO_EXTENSION);
 if(in_array($extension, array('jpg', 'png', 'jpeg'))){

  if(copy($_FILES['avatar']['tmp_name'], $avatar)){

   $sql = "INSERT INTO `login` (Firstname, Lastname, Email, Username, Password, Avatar) VALUES ('$firstname', '$lastname', '$email', '$username', '$password', '$avatar')";



   $result = mysqli_query($connection, $sql);
   if($result){
    $url = "../index.php";
    $messageok = "User registration succesfull!";
    echo "<script type='text/javascript'>alert('$messageok');</script>";
    echo '<script>window.location = "'.$url.'";</script>';
    

   }else{
    $url = "../index.php";
    $messagenok = "User registration failed!";
    echo "<script type='text/javascript'>alert('$messagenok');</script>";
    echo '<script>window.location = "'.$url.'";</script>';
   }
  } else{
    $url = "../index.php";
    $messageok = "Picture was not uploaded to database! plz try again";
    echo "<script type='text/javascript'>alert('$messageok');</script>";
    echo '<script>window.location = "'.$url.'";</script>';
   }
 }else{
    $url = "../index.php";
    $messageok = "Uploaded images must have one of following extensions, jpg, jpeg, png. Please try again!";
    echo "<script type='text/javascript'>alert('$messageok');</script>";
    echo '<script>window.location = "'.$url.'";</script>';
  }
   
}?>

<?php session_start(); ?>




<div class="popupscreen" id="registerpopup">
 <div class="formwrapper">
  <div class="login-form">
  <form action="includes/register.php" method="POST" enctype="multipart/form-data">
   <label class="popuplabel">First-name</label>
   <input name="firstname" placeholder="first-name" class="popupinput" required />

   <label class="popuplabel">Last-name</label>
   <input name="lastname" placeholder="last-name" class="popupinput" required />

   <label class="popuplabel">Email</label>
   <input name="email" placeholder="email" class="popupinput" required />

   <label class="popuplabel">Username</label>
   <input name="username" placeholder="username" class="popupinput" required />

   <label class="popuplabel">Password</label>
   <input name="password" placeholder="password" class="popupinput" required/>

   <label class="popuplabel">Upload profile picture</label>
   <input type="file" name="avatar" accept="image/*" />

   <button class="popupbutton" type="submit">Register</button>
  </form>
   <button onclick="closeregister()" class="popupbutton">Close</button>
 </div>
  
 </div>
</div>