You can only use the masthead on 1 server. Don’t use your existing licnse on a another server as you could cause mayhem in your current production environmnet (client resets due to epoch date changes against the existing FQDN).
To have a DEV/PROD setup you can use the licnesing centre to reallocate licneses to a new masthead, eg say move 10 or 20 from your existing serial number, create an new serial then allocate those spare licneses to that and create a new masthead/activation key. You can then build a standalone DEV server with that masthead so you have an enviromnent you can use for testing and test endpoint can be switched to use the new test environment .