Format: ansLength: ...999Variable (LLLVAR — 3-digit length prefix)
DE 63
Reserved — Private (Network Data)
What it is
Private use. Mastercard: network data (financial network code, Banknet reference). Visa: V.I.P. private-use field (network ID and message reason data).
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.