Login to your cPanel account and look at the left side of the page where it says "General Account Information."

It will then list what has been used and how many of each feauture you have left. Notice how the below examples says 0 / 0.

MySQL Databases 0/0

That means you are trying to add something your account doesn't have.

You need to go into your WHM create a new hosting package or edit an existing one that has the features you need.

After creating this package with the features you need, upgrade your site to the new or updated package.