Why doesn't the burger work?

Question

Bootstrap

When resizing the browser window, the burger does not work, what could be the problem?
the code:

<header class="header bg-dark">
        <div class="container">

            <nav class="navbar navbar-expand-lg navbar-dark bg-dark ">
                <a class="navbar-brand" href="#"> <h1 class="logo">.ONETOWN</h1>  </a>
                <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNav"
                    aria-controls="navbarNav" aria-expanded="true" aria-label="Toggle navigation">
                    <span class="navbar-toggler-icon"></span>
                </button>
                <div class="collapse navbar-collapse nav-header" id="navbarNavAltMarkup">
                    <div class="navbar-nav text-uppercase">
                        <a class="nav-link" href="#">Our works <span class="sr-only">(current)</span></a>
                        <a class="nav-link" href="#">about us</a>
                        <a class="nav-link" href="#">testimonials</a>
                        <a class="nav-link" href="#">subcribe</a>
                    </div>
                </div>
                <button type="button" class="btn btn-outline-light">JOIN <img src="./images/arrow-join.png" alt="">

                </button>
            </nav>
        </div>
    </header>