Does the join pop up also have an URL

Is there a way i can use an URL so that the join pop up starts?

I want to have a landing page with a button that links to the join pop up and not to join.php.

Thanks for your effort.

Instead of URL you can call JS function to open join popup:

<a href="javascript:void(0);" onclick="showPopupJoinForm();">Click to join</a>

I use mobirise to build the landing page. I can only enter an url. 

In which type of file do i have to implement (i assume) this code :  showPopupJoinForm();

maybe an  xyz.js file for javascript?  

I repeat the situation. User shall press button (join) on an external landing page, and then the join pop up of dolphin shall appear.

You can include inc/js/functions.js file and define Dolphin site URL in HEAD section of your page:

<script type="text/javascript" language="javascript">
    var site_url = 'http://yourdomain.com/path-to-dolphin/';
</script>

Then you will be able to call showPopupJoinForm function anywhere on the page.