Website is down in 360 Monitoring: unable to get local issuer certificate

Symptoms

• Website is down in 360 Monitoring with the following error:

  [60] SSL peer certificate or SSH remote key was not OK (SSL certificate problem: unable to get local issuer certificate)

• Public SSL checkers show that an intermediate certificate part in a certificate chain.

Cause

Missing CA certificate(s).

Resolution

Contact a certificate authority that issued the certificate and ask for the missing CA certificate(s), then install it.

In case this website is located on Plesk server, then the following can be done to install the missing certificate part once you have it:

1. Go to Domains > example.com > SSL/TLS Certificates > Download or remove existing certificates.
2. Add the missing CA certificate(s) into the field CA certificate (*-ca.crt) under Upload the certificate as text for the existing certificate.

Plesk article for reference: How to install an SSL certificate from 3rd party certificate authorities for a domain in Plesk?