How do I issue a free Let's Encrypt certificate?

The domain must resolve to this hosting server before certificate validation can succeed.

Steps

1. Open Websites & Domains.
2. Open SSL/TLS Certificates for the domain.
3. Select the option to get or install a free certificate.
4. Enter a monitored email address.
5. Select the domain names that already point to this server, such as the main name and www name.
6. Request the certificate, then open the site with https:// and check it loads without a warning.
7. Once HTTPS works, turn on Plesk's option to redirect visitors from HTTP to HTTPS.

If validation fails, correct the public DNS records or remove names that do not point to this server, then retry.