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Follow the steps to open the door as an admin without a booking (KeyMaster - PoolCar Administrator User Guide - Self Help - Confluence (atlassian.net)
Run a Status Inconsistency Report to ensure all the keys are synced with the bookings (Febin Joy what is the case if there is a key with a checked-out booking)
Permanently remove all keys from the cabinet before replacing.
Disconnect power
Plug the new head unit into the power source.
From the main menu, set up the network settings KeyMaster - PoolCar Administrator User Guide - Self Help - Confluence (atlassian.net)
Does the admin have to insert the keys back into the same slot in the old head unit? (Febin Joy)