These instructions came with my new digital banking card-reader:
This step enables the Card-Reader to provide a random code to help authorise your transation. On the Card-Reader screen you will see the following message: Enter Number
When you are prompted to use the Card-Reader during your Digital Banking session, two numbers will be displayed on screen. Check the last 4 digits of the authorisation number to ensure they are the same as the last four digits of the account number you wish to pay (or the fixed 8 digit reference number if you do not have an account number). Enter the authorisation number exactly as shown into the Card-Reader and press the OK key. The Card-Reader will then automatically generate a unique number on its screen: Enter this unique number generated by the Card-Reader into your Digital Banking page and follow the on-screen instructions to authorise your transaction(s).
I’ve read that three times, and I think I’ve now got it.