OptionalcodeMachine-readable error code (e.g. 'invalid_type', 'too_small').
OptionalexpectedWhat was expected (e.g. 'number').
Human-readable description of the problem.
Dot-path to the field (e.g. ['address', 'zip'] or ['amount']).
OptionalreceivedWhat was received (e.g. 'string').
A single validation issue — one field, one problem.