Certificate is not trusted by browsers.
One of the certificate roots that are in your website’s certificate trust chain is not being sent by your server or web host.
- Update your server configuration so that it includes the certificate’s trust chain as well as your website certificate.
One of the certificate roots in your chain of certificates has been revoked by the company that is responsible for that certificate.
The TLS Security Certificate being served by your server or web host have been revoked by the company that issued your certificate.