lightning cable doesn't fit into back of old iMac.
Have old iMAC and wireless keyboard broken so replaced it today with new magic keyboard. It is not showing on Bluetooth list to allow me to go through pairing process. I can however type whilst it is plugged in to an older cable that fits into rear of my iMAC ok. How can I move forward please. I am not technically minded whatsoever and thought it would be a simple process. Easy solution please.
iMac 27″, macOS 10.13