The error code is passed in the errorCode parameter of a response.
CANCELED = 0
GENERAL = 1
// processing-related
PROCESSOR_RKI = 32
PROCESSING_UNAVAILABLE = 40
PROCESSING_TX_INVALID = 41
PROCESSING_TX_DECLINED = 42
CARD_READING = 50
CARD_REMOVED = 51
CARD_PIN = 52
// for the PIN pad client library
SETUP = 5
CONNECTION = 10
DATA = 20