Well, this is actully the solution and he had some file missing like error.php from public_html and some files from public_html/admin. After I did what you advised him to do, I updated the Invision Suite directly from Applications/System. When I pressed Update Now, I couldn't contiune without some files which. After that I downloaded again the Invisioncommunity Suite from client area and I replaced the files that are missing, I pressed contiune and everything worked perfectly.
Not just that he's php version was running on 7.2 but I helped him change it to 8.0, after I changed it to PHP Version 8.0 the platform started working correctly.
And I did something else aswell from "Support" there were some recomandations and some criticals error which could be solved only with a click.
