1- Access the Plesk administration interface using your credentials.
2- In "Sites Web & Domaines", on the "Sécurité" section, click on "Certificats SSL/TLS".
3-In the certificate details view, click "Installer".
4- A window will appear asking you to secure your domain name and subdomains ( www, mail...), please check the corresponding boxes and then click on "Obtenir gratuitement"
5- Before clicking "Recharger", check if the TXT record has been added and the external resolution works.
6- Once the TXT record is verified, the SSL certificate will be automatically issued and installed on your account.