How to create a flow rule to block certain customers from placing an order?

Hello, I want to block some customers from placing an order in the store. How can I do this with flow?

Thanks!

Here is a template for deny-listed email addresses that might help you get started.

Yes, that is a solution which cancels already placed order. I’m trying to prevent the order from being placed in the 1st place.

Flow does not work/run in checkout. Apps that use Functions and work in checkout would be required to do that.