Whats wrong with this PHP code?

Hello! I am trying to paste this code in custom_functions.php, but I keep getting an error. I then have to remove the code through my cPanel. One thing to note is that I am placing this code at the very end of custom_functions.php .. Any help is appreciated!

function expiredpost(){
  if(in_category('expired')){
  ?>
    <div class="expired_img">
        <? echo "<img src='https://www.freebieshark.com/wp-content/uploads/2012/02/expired2.png'>"; ?>
     </div> <?
 }
}
add_action('thesis_hook_before_post', 'expiredpost');