Stand-In Ledger (SIL)

What it is

The Stand-In Ledger is a local, offline-safe ledger that lets the bank keep transacting while the Core Banking System (CBS) is unavailable (scheduled maintenance, network outage, vendor downtime, etc.).

Every transaction posted to SIL is recorded as a double-entry with full audit, idempotency and retry semantics. When the CBS is back online, a background worker automatically replays the pending transactions to core in the order they were posted.

Naming

The feature is known to the business as SIL (Stand-In Ledger). In code and APIs the prefix SIT is used (Stand-In Transactions). The two names refer to the same module.

Why it exists

Without SIL	With SIL
Tellers must turn customers away when CBS is down	Tellers continue serving customers
Reconciliation is manual after every outage	Replay is automatic and idempotent
No audit trail for offline activity	Every leg, idempotency key and retry attempt is persisted
Risk of double-postings on retry	Idempotency keys + transaction references prevent duplicates
Balance drift between branch and core	LastCoreSyncBalance + LastCoreSyncAt make drift visible

Module surface

The SIL module exposes commands grouped into five areas:

Area	Commands	Doc
Account & customer lookup	Search account, get balance, list accounts, list customers, mandate search	Account Management
Account state	Block, Unblock, Sync from core	Account Management
Financial transactions	Deposit, Withdrawal, Transfer, Loan Repayment, Reverse	Transactions
Approval workflow	Approve, Reject	Approval Workflow
Sync & replay	Sync transaction, Sync account, Hosted worker	Sync and Replay
Test data	Seed customers + accounts	Seed Test Data

For the underlying state machine and the rules every command must obey, read Account States and Rules first.

Command dispatch

All SIL commands are dispatched through the standard BankLingo command endpoint:

POST /api/cmd
Content-Type: application/json
Authorization: Bearer <token>

{
  "cmd": "SITDepositToTillCommand",
  "data": { ... }
}

The response shape is the BankLingo standard CommandExecutionResponse:

{
  "isSuccessful": true,
  "statusCode": "00",
  "message": "Posted to SIT.",
  "data": { ... }
}

Status codes follow the platform convention: 00 = success, 400 = bad request, 404 = not found, 409 = state conflict (e.g. account frozen), 503 = core banking unreachable.