[Membership 2 Pro] Membership plugin login is redirecting to wrong URL


I have set up the Membership plugin, but it seems it uses a wrong URL in the redirection, when somebody clicks on a restricted content.

This is the page, I'm talking about:

Steps to reproduce the issue:
1. Click on the webpage.
2. Click on a restricted article in the slider.
3. Redirecting to the login page.
4. Check the URL in the browser bar, where the "redirect_to" parameter has a wrong URL: apollonia.pjtsu.com

The URL is the server's main URL, but it is not set anywhere in the database or the wp-config file. Nowhere! I even don't know, how it could read this URL???

So the redirection is wrong. The installation is a Multisite, so the redirection is pointing to the main site's error message, when it says, there is no such a website in the network.

Please let me know, where this information is coming and why it is using this URL?