@Varun-Ganesh-D Glad you got it sorted out.
If anyone else is having similar issues, please consult the nginx configuration page in the NodeBB Documentation
I don't know what's happened. Yesterday its was working fine, but I did some changes that can be the cause of the problem. I will say what I did.
Today we deactivate and remove the plugins and Cloudflare, rebuild and start the server again, but the problem remains. I still have the option to only login with ssh keys in the server.
@baris Yeah, I just checked and had disabled the registered user to have local login permission. But I think I checked verified and unverified user to have the privilege. But why that will cause a problem? I was obviously login as a guest. Why that permission would affect a guest user? The problem was solved btw :).
Thanks in advance for the help. I just want to know how nodebb works.