This article will guide you through creating the super-flat world for your server.
Log in to your WiseHosting Game Panel here and Stop your server.
Click on Properties from the Game Panel tabs, and the World sub-menu from there.
Find the box level-type and change it to "minecraft\:flat" (default: minecraft\:normal).
Now to generate a new world, find the box level-name and change it to your desired name (default: world). Inserted information gets saved automatically.
Start your server from the Dashboard.
Congratulations! When the server has loaded up, you have created a new super-flat world!