option to pay has gone from App store on Mac after Tahoe upgrade

After upgrading to Tahoe a few days ago, I've just noticed that if I go to the App Store to buy something, after I click on the price button to proceed with payment, the dialog which follows gives me all the details of what I'm buying but no option to actually pay. There used to be the button where I could click and do the fingerprint recognition, but that's not there any more. I've tried with several apps and nothing. Note, this isn't a problem with updating apps I've already bought - I just can't get new ones. I researched it, and the common causes of not being able to pay are expired credit cards or unverified methods of payment - it's not that (I've checked). Also, please, I have re-booted the machine, and checked whether there are any pending updates which may be causing the issue... nada.

Does anyone else have this issue, or have a suggestion for how to solve?

Thx