Bootstrap nav bar does not collapse. How to fix this?

Here is my code. The navigation side bar remains open and does not collapse when I click the button.

Toggle navigation

        <a class="navbar-brand" href="index.php">ZM Corporation</a> 
     </div>
         <div align="right">
         <li><i class="fa fa-user align-right"></i> <?php echo $username;?></li> 
         </div>

        <?php include("navigation.php"); ?>

    </nav>