One of the TLS/SSL certificates used by your server is about to expire.
Once the certificate has expired, most web browsers will present end-users with a security warning, asking them to manually confirm the authenticity of your certificate chain. Software or automated systems may silently refuse to connect to the server.
This alert is not necessarily caused by the server (leaf) certificate, but may have been triggered by an intermediate certificate. Please refer to the certificate serial number in the alert details to identify the affected certificate.
Contact your Certificate Authority to renew the SSL certificate.