The error is shown when connecting to a server via FTP:
CONFIG_TEXT: The server's certificate is unknown. Please carefully examine the certificate to make sure the server can be trusted.
Valid from: xx/xx/xxxx
Valid to: xx/xx/xxxx - Certificate expired!
Plesk uses expired certificate.
Log into Plesk and use Let's Encrypt extension at Plesk > Tools & Settings > SSL/TLS Certificates > Let's Encrypt as described at How to secure Plesk login page with SSL certificate article. It will create a new certificate.
Another possible solution is to create and use self-signed certificate:
- Open Plesk > Tools & Settings > SSL/TLS Certificates > Add
- Fill in the necessary information.
- Click on Self-Signed.
- In Certificate for securing Plesk click Change and select the new certificate.