Hi,
Thank you for posting your query.
Kindly follow the steps provided below to resolve your issue.
You have to choose new private key. You cannot install same CA twice. That is, you cannot take a backup of existing subordinate CA and deploy it in another site. You have to install a brand new subordinate CA (with different name) under existing root. Follow same guide you used to deploy existing subordinate CA.
Go to this link for your reference and other troubleshooting procedures https://learn.microsoft.com/en-us/answers/questions/666853/adding-a-subordniate-certificate-authority-to-an-e
Do not hesitate to message us if you need further assistance.
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