HELP ME WITH THIS PROBLEM

Have you populated the database with default data, is this a fresh install?

This seems to me that you have no default data, so you would need to add it to MongoDB

6. Seed/populate the MongoDB with some default data

Navigate in terminal(putty) to the applications seed folder

cd /var/www/html/app/seed

Seed/Populate the MongoDB

nodejs dbseed.js

If this doesn't work change this line in dbseed.js on your server

https://github.com/byNeHo/CoD4x-WebAdmin/blob/master/app/seed/dbseed.js#L10

to this

mongoose.connect(dbURI, {useNewUrlParser:true});

I have removed this part " , useUnifiedTopology: true "

After you remove ", useUnifiedTopology: true" from that line try to run again this part

Navigate in terminal(putty) to the applications seed folder

cd /var/www/html/app/seed

Seed/Populate the MongoDB

nodejs dbseed.js