SambaPOS interoperability between Win10 and Win7 works. This will not cause an issue.
ONLY the “Server” should have SQL Express (full, non-LocalDB edition) installed as well as the MessageServer Service.
NOTE: the Message Server has nothing to do with DB connectivity, but is required for multi-terminal setups anyway, since it is responsible for terminal-to-terminal communication.
Other “client” Terminal machines do NOT require DB installation, nor do they require installation of the MessageServer Service. In fact, installation of DB and Message Server Service on “client” Terminals other than the “Server” will cause issues, guaranteed.
I think most of the Tutorials on multi-terminal are very good. This is the best:
Some good information on DB connection testing and issues is here:
When it comes to Message Server problems and DB connectivity problems, this Topic gives a great amount of detail into investigations and resolutions: