The register is currently in void mode and it has been closed because the last user has signed out. You need to sign back on to the machine using your secret PIN number. If you have lost or don't know it, you can program the clerk numbers with the manual:
https://the-checkout-tech.com/manuals/cashregisters/Samsung_ER-420M_operating_programming_manual.html
Registerman
February 2016
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