Hello.
As I remember I did the following:
All machines had no Retail manager prior or hard disk been formatted,
Before connecting to local network, I installed from original CD complete RMS (SQL, Manager, Admin, OPOS) with PID that was with the original CD,
Created a database from an old backup and connected as local, with Administrator, once connection established I tested the Manager
Then opened OPOS and hit the register over the net. Did not ask for any keys or anything, just gave "success".
Then established a connection to network server. One think I found necessary, was if the machine is on Windows XP and the others are Win 7 or 10 (we never had any 8s) the first network connection should be attempted from XP machine.
We have all mixture of windows all happily running Manager and Administrator but cash registers are on XPs and 7s.
I hope this can help.