Optional
This field specifies the reference to the entire message assigned by either the:
initiating institution, when present or
ordering institution, when the initiating institution is not present.
This field must not start or end with a slash '/' and must not contain two consecutive slashes '//' (Error code(s): T26).
When this field is present, the ordering institution requests a single debit entry for the sum of the amounts of all transactions in the instruction, even if this instruction is chained in several messages. If the field is not used, all debit items are posted individually.