Spending controls in a cashless society.
Hmm. Good potential here for a chrome dystopia.
We could imagine some harsh sci-fi scenario in which a theocratic regime issues decrees to payments processors to block anyone buying books deemed sexually deviant. Such decrees could be automatically enforced via code, with subroutines remotely triggering smart locks to place the offending miscreant under house arrest while automatically deducting a fine from their account