Staging site does not work

I wonder whether you can help me. I have set up a staging site but it is not working. When I go to view the staging site the homepage doesn’t work load properly, it’s just a series of symbols and hyperlinks. There is no orange staging site banner at the top of the page. By navigating to the “shop” page I am able to find the original site with the orange staging banner but can do nothing else. If I try to head to wp admin then I just get a 500 server error.

Is this a known problem? How can I fix it in order to successfully use the staging site?