pm2 config json gives 502 Bad gateway

Question

I am using pm2 for my node server. My pm2 config json is as follows

{
    "apps": [{
        "name": "hello",        
        "script": "server/app.js",
        "exec_mode": "fork",
        "env": {
            "NODE_ENV": "development",
            "PORT": 9000
        }
    }]
}

I am starting the application using: pm2 start pm2Config.json

My application is showing online but not loading. When I try to access the application, it is giving me 502 bad gateway error. But nothing is coming in the logs.

I don't know what went wrong. Please help.

Thanks in advance.