@New-Cyan-Starfish-1965559618#192695 The payment you can do however you want. With a physical card, Apple Pay/Google Pay or on Android also with the bunq App itself (the feature is called Tap & Pay then).
Just to make sure we're not conflating anything here, 1) you can have different sub-accounts for different purposes (all with their own IBAN), 2) and there is also the feature called Insights, which let's you assign categories to your expenses (from a pre-defined list that is not editable).
For 1): You can select any of your cards and assign them / connect them to a different sub-account whenever you want. While they're connected to a certain account, all purchases that you then make with that card, be it with the physical card or via a phone, will get deducted from that account. So before you go to the supermarket (or while waiting in line at the checkout), you could get out your phone and connect one of your cards to your sub-account that you only use for Groceries spending. Then when you pay with that card at the supermarket, the money will get deducted from that account. But let's say you make a mistake and you pay at the supermarket checkout with the card still connected to another sub-account of yours, then you cannot change that back. The payment has already been made and deducted from that account. The only thing you can do then is transfer money between your accounts.
For 2): The Insights feature is not real budgeting, it merely allows you to track your expenses. On the [Profile] tab you will be able to see a monthly pie chart that shows how much you have spend in certain categories. The good thing here is that you can always change the category that a certain payment is assigned to, and the payments are also automatically assigned to a fitting category. What you cannot do is set a certain spending limit or goal to such a category.
Does that make it clearer?