Installation the module does not take longer than 10 minutes.
- Extract the module archive which you downloaded from the client area.
- Upload the module to your WHMCS installation.
- Go to the WHMCS Admin backend, click on Setup → Addon Modules and activate the module.
- Click on Configure.
- Enter your license key, choose the newly created custom field at the dropdown, select Full Administrator at "Access Control", click on Save Changes.
- Now, some new dropdowns appears. Select at the dropdowns the correct option and click Save Changes again.
It should look like on this screenshot:
Custom Fields: Follow this guide to setup the custom fields.