Can't secure Plesk with Let's Encrypt: Invalid port in redirect target. Only ports 80 and 443 are supported, not 8443

Symptoms

• Let's Encrypt fails to secure the Plesk panel

  Invalid port in redirect target. Only ports 80 and 443 are supported, not 8443

• The hostname used to access the panel isn't served by Plesk and is absent from the domains list

• A redirect is configured in /var/www/vhosts/default/htdocs/.htaccess

  Redirect / https://example.com:8443/login_up.php3

Cause

Custom redirects configured for the Plesk hostname prevent Let's Encrypt from accessing the panel.

Resolution

1. Connect to the server via SSH

2. Edit /var/www/vhosts/default/htdocs/.htaccess and remove the redirect line

   # vi /var/www/vhosts/default/htdocs/.htaccess

3. Follow this article to make Plesk accessible over a hostname: How to customize the Plesk URL

4. Issue the Let's Encrypt certificate