> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lead.bank/llms.txt
> Use this file to discover all available pages before exploring further.

# Internal Transfer Sandbox Testing

> Test internal transfers in Lead's sandbox environment.

Internal transfers need no simulation endpoints and no setup. Create a transfer with `POST /v1/internal_transfer` and it processes automatically: within seconds it moves from `processing` to `posted` and fires the `internal_transfer.posted` webhook, the same sequence you'll see in production.

## What's Different From Production

The sandbox is not connected to a ledger for this rail, which has two consequences:

* **Every transfer succeeds.** No balance checks run, so you don't need to fund the sender before testing, and you can't trigger a rejection like `non_sufficient_funds`. Build your rejection handling from the webhook and rejection reasons documented in [Handling Failures](/products/internal-transfer/exceptions); the `internal_transfer.rejected` event can't be produced in sandbox.
* **Balances don't move.** A posted transfer doesn't change the sender or receiver balance, so don't reconcile balances against internal transfers in sandbox.

Synchronous request validation still applies: an invalid request, such as a transfer between two Account Numbers under the same Account, returns a `400` the same way it does in production (see [Sending an Internal Transfer](/products/internal-transfer/sending)).

## Test the Happy Path

1. Create the transfer with `POST /v1/internal_transfer`. The 200 response returns the transfer in `processing`.
2. Within seconds, the transfer moves to `posted` and fires the `internal_transfer.posted` webhook. No advancement call is needed.