Optional
On an AWAITING_SIGNATURE row, the external signers (base58), in message order.
AWAITING_SIGNATURE
Base64 wire transaction: fully signed, or on an AWAITING_SIGNATURE row the unsigned message for the external signers. Absent on a CANCELLED row.
CANCELLED
On an
AWAITING_SIGNATURErow, the external signers (base58), in message order.