Bootstrap 4 modal with responsive iframe

[admin]

I tried to make a modal with an iframe.

<a href="#" data-toggle="modal" data-target="#exampleModal">
<img id="imageresource" src="http://www.justdeluxe.at/wordpress/wp-content/uploads/2019/01/nature-3048299_1920.jpg" style="width: 400px; height: 264px;"></a>  


          <div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel" aria-hidden="true">
            <div class="modal-dialog" role="document">
              <div class="modal-body">
                  <iframe src="https://player.vimeo.com/video/80836225?badge=0" width="640" height="360" frameborder="0" allow="autoplay; fullscreen" allowfullscreen></iframe>
              </div>
            </div>
          </div>

What I found out is, when u remove the

<div class="modal content">

I have my iframe perfectly responsive.
The problem is, that I cant play the video. So the iframe doesn't responsive when clicking.

Does anyone know why?

The original code for the modal was this: <a href="https://getbootstrap.com/docs/4.0/components/modal/" rel="nofollow noreferrer">https://getbootstrap.com/docs/4.0/components/modal/</a>

<div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel" aria-hidden="true">
  <div class="modal-dialog" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <h5 class="modal-title" id="exampleModalLabel">Modal title</h5>
        <button type="button" class="close" data-dismiss="modal" aria-label="Close">
          <span aria-hidden="true">×</span>
        </button>
      </div>
      <div class="modal-body">
        ...
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
        <button type="button" class="btn btn-primary">Save changes</button>
      </div>
    </div>
  </div>
</div>