Your .NET hosting plan includes a free SSL certificate from Let's Encrypt. Before installing your SSL certificate ensure that your domain is pointing to the server otherwise the certificate cannot be issued.
Install your free SSL Certificate
- Login to your Plesk account and view your domain name
- Make sure you are on the Dashboard tab:

- Under security you will see the following:

- If your SSL/TLS Certificates has an error or warning, click on the icon to open the SSL settings page.
- Scroll down to the bottom and click on Install for your free Let's Encrypt certificate.

- Tick the required boxes and click on the Get It Free button

- Follow the onscreen instructions to complete your SSL installation