If you have not yet created a Certificate Signing Request (CSR) and ordered your certificate, see
SSL Certificate CSR Creation :: Plesk Server. Step 03 :
Installing your Plesk Server SSL Certificate
Download the Primary, Intermediate, and Root certificate files from your DigiCert account.
Login to the Plesk Control Panel.
Select ‘Domains‘ from the left hand menu.
Click on the domain name that the certificate is for.
Click on the ‘SSL/TLS Certificates’ menu item.
Add SSL/TLS Certificate
You will have the option to either “Upload certificate files” or “Upload certificate as text.” Either way will work fine for your purposes.
Plesk Tools & Settings Screen
Step 04 :
Click the Add button.
SSL Certificates Screen
Step 5
Fill out the required fields. In the Domain name section, be sure to write out the domain or subdomain the Certificate is for. The SSL will not be configured correctly if it was ordered for www.domain.com and it is set up in Plesk as only domain.com Copy and paste the full Private key and Certificate into the respective text boxes, or use the Browse button to upload the certificate and private key. When all the fields have been completed, click the Upload Certificate button.
also fill this form/page, with , Private key (*.key) *, Certificate (*.crt) * and then CA certificate (*-ca.crt) and click on upload,
Add SSL Certificate Screen
Step 6
You are taken back to the SSL Certificates page in Plesk and informed the SSL was added successfully. You will also see the SSL certificate name you had chosen in the list below.