Context A multi-step payment flow has complex state transitions (idle to validating to processing to success or failure) with conditional logic and side effects. The Problem The current implementation uses multiple useState booleans that can reach impossible combinations, causing intermittent UI bugs. Constraints Model the payment flow as an XState state machine with explicit states and transitions. Integrate the machine with React using useMachine. Guarantee that impossible states cannot occur. Expected Deliverable A React payment flow component driven by an XState state machine, eliminating impossible state combinations and providing predictable UI transitions.