Unable to remove a certificate in Plesk: One or several certificates are assigned to the IP addresses or domains

Check if SSL was used to secure site's webmail:

1. Log in to Plesk
2. Open Domains > example.com > Mail Settings
3. If SSL is selected to protect webmail, un-check it
4. Remove SSL in Domains > example.com > SSL/TLS Certificates

Find an IP address where SSL is used:

1. Log in to Plesk
2. Go to Tools & Settings > IP Addresses > open IP > check SSL/TLS certificate section for each IP address. If SSL that is required to be removed is assigned to an IP address, switch (change) it to a different SSL or to default certificate:
   

Find if there are other domains using the same SSL:

1. Connect to the server via SSH on Linux or via RDP on Windows
2. Backup Plesk database
3. Login to Plesk database
4. Retrieve the certificate ID:

   MYSQL_LIN: select id, name from certificates where name = 'test_ssl';
   +----+-----------+
   | id | name |
   +----+-----------+
   | 7 | test_ssl |
   +----+-----------+
   1 row in set (0.00 sec)

   'test_ssl' is the name of the certificate that you are trying to remove. It can be checked at Domains > example.com > SSL Certificates > Name:

   

5. Find all domains that have the same SSL assigned:

   MYSQL_LIN: select d.name from domains d inner join hosting h on h.dom_id = d.id where h.certificate_id = 7;
   +----------------------+
   | name |
   +----------------------+
   | example.com |
   | example2.com |
   +----------------------+
   2 rows in set (0.00 sec)

6. Log in to Plesk
7. Open Domains > example2.com > Hosting Settings and switch "test_ssl" to "Not Selected".