MT581: (2) Field 21: Related Reference
This field specifies the related reference.
NETWORK VALIDATED RULES
This field must not start or end with a slash '/' and must not contain two consecutive slashes '//'.
This field contains the reference number assigned by the Receiver to the related securities loan, for example, the contents of field 20 Transaction Reference Number of the MT 516 Securities Loan Confirmation received or the contents of field 20 Transaction Reference Number of the previous MT 581 received.
If the Receiver's reference is not known, NONREF must be used in this field.