Warning: The players.json endpoint has been modified

[ citizen-server-main] Warning: The players.json endpoint has been modified to no longer return the player identifiers without authentication.
[ citizen-server-main] To learn more about this change read our announcement at Celebrating one year with Rockstar Games - Cfx.re Announcements - Cfx.re Community.

I keep getting an error message like this in the log, which is probably why the screen is still black after I’ve selected a character.
Can someone please tell me what’s going on?

The first thing from that message is “Warning” which is not the same as an error. This warning has no effect on anything in the server (unless for some reason you use it for information which you shouldn’t).
If you have a black screen after selecting a character then you likely have an error in one of your resources.

Thank you for telling us.
By the way, I don’t see any error codes when I open the console or F8.
Is there something else causing this?

Welcome to scripting where something can break without throwing an error…
You have an issue with some resource on your sever (or lack there of) to fade in the screen (remove the black screen). Unfortunately, there’s not much I can help with.

I see. I understand.