The regular Repetier-Server Pro license allows you to use one license for up to 5 installations and run them simultaneously. This is to run all your printers and to outsource compute-intense work to faster PCs – high quality rendering of big models is not really fun on a Raspberry Pi.
Licenses are always licensed to one user! It should be obvious that if multiple persons know the key, one of them can try to install it multiple times preventing the other users from installing it on their devices. If one user resets the license, he can use all 5 installations and all other users can not reactivate their server. So sooner or later you are asking for trouble if you split a license. For this reason, we strongly advise against buying second-hand licences!
If you are a printer manufacturer you can talk to us about possible solutions.