OK The OTP is valid. BAD_OTP The OTP is invalid format. REPLAYED_OTP The OTP has already been seen by the service. BAD_SIGNATURE The HMAC signature verification failed. MISSING_PARAMETER The request lacks a parameter. NO_SUCH_CLIENT The request id does not exist. OPERATION_NOT_ALLOWED The request id is not allowed to verify OTPs. BACKEND_ERROR Unexpected error in Yubico servers. Please contact them if you see this error. NOT_ENOUGH_ANSWERS Server could not get requested number of syncs during before timeout. REPLAYED_REQUEST Server has seen the OTP/Nonce combination before. BAD_NONCE Answer Nonce is different from the request Nonce. CONNECTION_ERROR Impossible to make a connection with the YubiCloud servers. OTP_IS_DIFFERENT Answer OTP is different from request OTP. OUT_OF_TIME_WINDOW Timestamp difference with the Yubico servers is bigger than yubicloud_max_time_window. SERVER_TIMEOUT Timeout while waiting an answer from the server.