Q: why does my mouse 2 not get recognised by my mini mac?

Just bought a new mouse2 which isn't seen by the mini-mac. An old style wireless keyboard works fine as did a trackpad2 (switched off during attempted link up). Tried the 'connect bluetooth mouse' but not still not recognised. Mini-mac software update ℅, still the same. Switch at green position and linked up to known working usb socket using provided lead.