As mentioned in comments, the error should be pretty clear, you can't put it on a server it wasn't meant for.
For your UAT server, just use a self-signing certificate which is free. Your users will still get a warning in their browser that the certificate may be invalid but that is fine, it will still encrypt the data. See
https://technet.microsoft.com/en-us/library/cc753127(v=ws.10).aspx[
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