Popup not shown on many browsers

Hello Andreas. Do you see any errors in Javascript Console on the browser where it fails?

Please provide more information/steps to reproduce see for more information https://www.drupal.org/contributor-tasks/add-steps-to-reproduce

I had the same problem with the D8 version. I was using a Chrome version.
The fix was to set the Popup height in pixels value. If left blank the pop up would not appear. When I set it to 75px for example it appeared.

I think the problem is when you put the trailing slash at the end of url in the domain list. For instance: http://local.test/
The code compare the domain list with $base_url variable and remember the $base_url does not include the trailing slash

I removed the slash with the following code and works like a charm

    $domains_list = explode("\n", $domains_list);
    $domains_list = preg_replace('{/$}', '', $domains_list); // I added this line 
    $domain_match = in_array($base_url, $domains_list);

Regards!

Thank you sgonzalez11, I added your patch to -dev.