Sending book transfers

A book transfer moves money between two virtual accounts and produces two transactions: a debit from the source balance and a credit to the destination balance.

How to move money between virtual accounts

Both virtual accounts must belong to the same Account. Creating a book transfer requires a user API key with book-transfer access, used from an allowlisted IP. amount.amount is in minor units, so 250000 USD means USD 2,500.00.

curl https://api.slash.com/v2/transfers/book \
  -X POST \
  -H "X-API-Key: $SLASH_API_KEY" \
  -H "x-legal-entity: $SLASH_LEGAL_ENTITY_ID" \
  -H "X-Idempotency-Key: payroll-funding-2026-08" \
  -H "Content-Type: application/json" \
  -d '{
    "amount": { "amount": 250000, "currency": "USD" },
    "fromAccount": "subaccount_operations123",
    "toAccount": "subaccount_payroll123",
    "description": "August payroll funding"
  }'

The returned Transfer uses a transfer_intent_ id and lists both ledger legs. This example shows a completed transfer; a create response can instead be pending or in_review:

{
  "id": "transfer_intent_book123",
  "type": "book",
  "status": "settled",
  "accountId": "sa_group_primary123",
  "fromAccount": "subaccount_operations123",
  "toAccount": "subaccount_payroll123",
  "amount": { "amount": 250000, "currency": "USD" },
  "description": "August payroll funding",
  "transactionIds": [
    "agg_tx_booksource123",
    "agg_tx_bookdestination123"
  ],
  "createdAt": "2026-08-18T01:00:00.000Z"
}

Use GET /v2/transfers/book/{transferId} for the Transfer and GET /v2/transactions?transferId=… to reconcile both account impacts.

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Concepts

Money movement

Webhooks

Reference

Sending book transfers