Certificate issues in D365FO Cloud hosted environment

 The problem with certificates is that they have an expiry date.

Since all Dynamics environments are deployed using LCS and the Cert used is owned by Microsoft we have limited ability to fix the issue on our own. This is why Microsoft built functionality into LCS to help us with this. To fix the issue, just look up the environment in LCS, click Maintain and select Rotate Secrets

The Cert you need to fix is the SSL Certificate

Simply click Rotate SSL Cert and wait for the process to finish.