Format: nLength: ..11Variable (LLVAR — 2-digit length prefix)
DE 33
Forwarding Institution Identification Code
What it is
Identifies the institution forwarding the message when it is not the acquirer itself (e.g. a processor or gateway).
Specification reference
Defined in ISO 8583:1987 (base). Card networks publish their own dialect tables (Visa BASE I / V.I.P., Mastercard CIS) that refine formats, lengths, and — for private-use elements — the entire layout. Always confirm against the interface specification you implement.