Hi @Donb_21 ,
The error you mentioned can happen if TLS 1.2 is not enabled, since TLS 1.2 is now enforced by Azure. If this is the case, you need to make sure you run the following command prior to running Update-AzureADSSOForest
:
[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
See full steps for enabling TLS 1.2 on the server.
One solution I have also seen for that error is to copy the %programfiles%\Microsoft Azure Active Directory Connect folder to a non-server 2016 machine.
In addition, I would make sure that the account has the necessary permissions.
I would recommend checking the troubleshooting article here, since it is difficult to diagnose this based on the information provided.
If these steps do not work, it would help if you could provide more details about your scenario and any additional errors you receive so that I can better troubleshoot your exact issue.
If the information helped point you in the right direction, please Accept the answer. This will help us as well as others in the community who might be researching similar issues.