'Invalid MAC' error

Understand and clear an Invalid MAC message on your terminal.

What it means

'MAC' here is a security check between your terminal and the bank, not your network's MAC address. An Invalid MAC usually means the terminal's security keys need refreshing.

Power-cycle the terminal

Restart it (hold the yellow and full-stop keys). On start-up it re-checks in with the acquirer, which clears most one-off MAC errors.

Force a check-in

If your terminal has a 'logon' or 'check-in' option in the menu, run it — this re-syncs the keys with the bank.

Persistent error

If it keeps showing Invalid MAC, the keys need re-injecting. Call 0191 432 6588 and we'll sort it, usually remotely.

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