> For the complete documentation index, see [llms.txt](https://docs.flash.trade/flash-trade/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.flash.trade/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/concepts/how-transactions-work.md).

# How transactions work

You never assemble instructions by hand. Every write goes through the same shape:

```
POST /transaction-builder/{action}   →   unsigned transactionBase64
        │
        ▼
decode → sign (client-side) → submit to the right RPC → confirm
        │
        ▼
read updated state from the basket snapshot (not the response)
```

The build → sign → submit mechanics — decode code, which RPC, who signs, blockhash expiry — live on [Signing & submitting](/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/signing-and-submitting.md). This page covers the ideas behind them.

## Quotes vs. plain builders

* **Quote builders** (`open`, `close`, `reverse`, collateral) return a rich object — projected leverage, entry/liq price, fees — with the transaction under `transactionBase64`.
* **Plain builders** (triggers, limits, most funds ops) return just `{ "transactionBase64": "…" }`.

## Preview before you commit

Two ways to compute without spending anything:

* Omit `owner` on `open-position` → you get the quote back with `transactionBase64: null`.
* Use the [`preview/*`](/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/reference/previews.md) endpoints for fees, exit fees, TP/SL PnL, and margin changes — no transaction built at all.

## State is in the basket, not the response

A trade response is a *quote* of what will happen, not confirmed state. After a transaction confirms, read the truth from [`GET /owner/{owner}`](/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/reference/account-and-positions.md) or the [WebSocket](/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/reference/websocket.md). There can be brief lag between submitting and the committed state appearing.

## Two error surfaces

* **HTTP** errors (`4xx`/`5xx`) return `{ "error": "…" }`.
* **Compute** errors on quote endpoints return `200` with `{ "err": "…" }` in the body — a well-formed request the engine couldn't price.

Full matrix and recovery: [Errors](/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/errors.md).


---

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