You can easily create a free certificate in the Plesk web interface, which is also valid for all subdomains.  We describe how to do it. <br />
Request Wildcard SSL Certificate<br />
Log in to the Plesk web interfaceIn the list, find the domain to which you want to add an SSL certificate. Open the DNS management of the domain in the background.  Make sure that the domain is connected to your web hosting. In the Plesk web interface, click on &#8222;SSL/TLS Certificates&#8220; for your domain. Click on &#8222;Issue SSL certificateIn the sidebar that opens, select &#8222;Install free basic certificate from Let&#8217;s Encrypt&#8220;. In the window that opens, check &#8222;Protect wildcard domain (including www and webmail)&#8220;. Click on &#8222;Use for free&#8220; and wait a moment. A screen with the headline &#8222;SSL/TLS wildcard certificate from Let&#8217;s Encrypt is issued for domain XYZ&#8220; will open. Copy the cryptic looking string, for example &#8222;3fOObNS5sZSG4cJa01FOMHJcEyxW8BWCcivQGNNmO6Q&#8220; to the clipboard<br />
DNS Challenge string<br />
Configure DNS<br />
Open the DNS administration and click on &#8222;New entry&#8220;. Set:Type: TXTName: _acme-challengeContent: (your copied string)Save the entry<br />
Enter ACME Challenge in DNS<br />
Install certificate<br />
Go back to the Plesk administration interfaceClick on &#8222;Reload&#8220; in the dialog and wait a momentThe certificate will now be installed and activated for all subdomains<br />
If you have any questions or problems, please contact our support.  We will help you then!