I have done it right. use the # sign before the ID so that the navbar link will works. why do "Your file was not found" appear? I will include my HTML codes :
<
!-- Nav Bar -->
<nav class="navbar navbar-expand-lg navbar-dark ">
<a class="navbar-brand" href="#">Van-tag</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarTogglerDemo02">
<ul class="navbar-nav ml-auto">
<li class="nav-item">
<a href=" nav-link" href="#footer"> Contact</a>
</li>
<li class="nav-item">
<a href="nav-link" href="#pricing"> Pricing</a>
</li>
<li class="nav-item">
<a href="nav-link" href="#cta"> Download</a>
</li>
</ul>
</div>
</nav>
Here is the link of my full HTML codes. maybe it will helpful. https://code.sololearn.com/WI5eJj8HKGqH/#html