Can't connect to Web UI

so I installed and librenms on debian 9. Everything more or less went smoothly, but after finishing the steps on WebUI it gave me an error:

After checking unckle google (not much info there) of fixing it, it seems like I had a permissions problem, so I checked the permissions and gave to the whole folder root permission - without any kind of success. So I went then to the folder and check ./validate command. It seems there is more to problems than I imagined. With the permissions I “experiemented” a lot and tried to go with those which texted me in terminal. No matter what I did I was unable to fix those.
Could anyone help please? Thank you.

Another problems are located here:

User must be “librenms” and not root. Never ever run any LibreNMS script using root user.
Then, using validate.php, make sure that no more FAIL and WARN are around. And let us know where you are after that.