Old apple keyboard A1314 not pairing with my macbooks

Hello community

I have an apple keyboard A1314 (needs 2 AA batteries) that i used to use with my macbook.

Later, i bought magic keyboard and stored the old one away.

I now wish to give away the old keyboard to someone else and wanted to test it before giving away. Since then, I have also changed my macbook.

Now when i try to pair it with my macbook pro and macbook air, i get an error which says "Passkey mismatched" OR "pairing attempt was unsuccessful"

I get the first error when i try to connect the keyboard via bluetooth preferences.

I get the second error when i try to "Setup a new bluetooth keyboard"

Bluetooth is able to find the new device.

I wonder if the keys are working. How can i find out what is wrong and fix this. ?

Thanks