A1255 keyboard not pairing. Works fine with Windows laptop

I have a couple of A1255 original wireless keyboards that work fine with Windows laptops. I can find them under Bluetooth devices and connect fine. Whenever I try and connect to Mac devices, it fails to register keys pressed in order to pair.

I have read that these keyboards (if paired with another Mac) need to be unpaired on that mac before they can be successfully paired with another Mac. But surely there's got to be a way to overcome this as I don't know which Mac they were previously paired with and don't have access to those macs.

I've tried keeping the power button pressed throughout the process but still keys are not registered when enter keys to pair screen pops up

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