KMC keep saying "You must have flash installed. click here to download"

You need to make sure the hostname/service URL you provide during the configure phase is accessible from both the server itself and from any outside client you intend to use the admin I/Fs or playback from.
My guess is you provided a hostname/service URL that is NOT resolvable from the machine where you make the request from.
This can easily be checked by opening your browser's dev tools and looking at the requests made in the "Network" tab, then making sure the host used is resolvable.