First verify that the server name and port provided in the MDM integration basic setup under MC>Setting>Integrations>MDM/UEM/EMM>Basic Setup is correct.
If the information is verified to be correct, certificate errors can be checked for using open source tools such as curl, openssl, or https://www.ssllabs.com/ssltest/index.html
Depending on the identified cause, the solution may be to.
(NOTE: for assistance resolving these certificate issues on your on-premises MDM implementation, you should reach out to the CA)