"The certificate's Common Name or Subject Alternative Names contain an internal name."
Industry standards prohibit Certificate Authorities (CAs) from issuing certificates to internal names (see SSL Certificates for Internal Server Names). An internal name is an IP address or domain that is part of a private network (see RFC 2606). Validation can't be completed for internal names because they can't be externally verified.
Additionally, non-unique internal names carry too much potential for malicious misuse. For example, a CA can issue a publicly-trusted certificate to a company for https://mail/. Because this name is not a unique name, anyone else can get a certificate for https://mail/.
If you are a server administrator using internal names, you need to either reconfigure those servers to use a public name or switch to a certificate issued by an internal Certificate Authority. All internal connections that require a publicly trusted certificate must be done through names that are public and verifiable (it doesn't matter if those services are publicly accessible).
Depending on the applications in your environment, you may be able to reconfigure the application to not require internal names.
DigiCert is the world's leading provider of scalable TLS/SSL, IoT and PKI solutions for identity and encryption. The most innovative companies, including 89% of the Fortune 500 and 97 of the 100 top global banks, choose DigiCert for its expertise in identity and encryption for web servers and Internet of Things devices. DigiCert supports TLS and other digital certificates for PKI deployments at any scale through its certificate lifecycle management solution, CertCentral®. The company is recognized for its enterprise-grade certificate management platform, fast and knowledgeable customer support, and market-leading security solutions. For the latest DigiCert news and updates, visit digicert.com or follow @digicert.
©2020 DigiCert, Inc. All rights reserved. DigiCert, its logo and CertCentral are registered trademarks of DigiCert, Inc. Norton and the Checkmark Logo are trademarks of NortonLifeLock Inc. used under license. Other names may be trademarks of their respective owners.