In case anyone else has this issue, it was solved by making sure I started the application pools.
Lost Exchange connection to ECP and Admin Center

We have one single Hybrid 2016 server on our domain.
We were renewing the wildcard certificate it uses, and suddenly it rebooted. When it came back up, we got the attached errors for both the Shell and the Admin Center. There are no other Exchange servers for me to connect to on site.
Anything I would normally try requires access to one of these to work. Does anyone have any advice on how to get his back up and running? Thank you in advance,
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Andy David - MVP 120.5K Reputation points MVP
2021-09-08T18:02:00.123+00:00 Is your OAuth Cert expired?
https://learn.microsoft.com/en-us/answers/questions/476090/ex2019-cu10-owaecp-not-working-after-july-security.htmlIf you cant use remote powershell to fix, try using the snap-in from a regular powershell window. be careful, its not technically supported:
Add-PSSnapin Microsoft.Exchange.Management.PowerShell.SnapIn