> 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/signing-and-submitting.md).

# Signing & submitting

How to decode, sign, and submit the transactions the API builds.

There's no API key and the server never holds your keys. Every transaction-builder endpoint returns an **unsigned, base64-encoded versioned transaction** (v0). You decode it, sign it client-side, and submit it yourself.

## Which RPC?

Route each transaction to the correct endpoint or it will fail:

| Transaction kind    | Endpoints                                                                                                                             | Submit to           |
| ------------------- | ------------------------------------------------------------------------------------------------------------------------------------- | ------------------- |
| **Account & funds** | `init-*`, `deposit`, `deposit-direct`, `delegate-basket`, `withdraw`, `custody-settlement`, `withdrawal-settle`, `request-withdrawal` | your Solana RPC     |
| **Trading**         | `open`/`close`/`increase`/`decrease`/`reverse-position`, collateral, triggers, limits                                                 | the v2 RPC endpoint |

Set both up front:

```bash
export SOLANA_RPC_URL="https://api.mainnet-beta.solana.com"
export V2_RPC_URL="<v2-rpc-endpoint>"
```

## Decode, sign, submit

```typescript
import { VersionedTransaction, Connection } from "@solana/web3.js";

async function buildSignSubmit(path, body, signers, rpcUrl) {
  const res = await fetch(`${FLASH_API_URL}${path}`, {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify(body),
  });
  const data = await res.json();
  if (data.err) throw new Error(data.err);           // compute error in a 200 body
  if (!data.transactionBase64) throw new Error("preview-only or no tx");

  const tx = VersionedTransaction.deserialize(
    Buffer.from(data.transactionBase64, "base64")
  );
  tx.sign(signers);

  const connection = new Connection(rpcUrl, "confirmed");
  const sig = await connection.sendRawTransaction(tx.serialize());
  await connection.confirmTransaction(sig, "confirmed");
  return sig;
}

// Trade → v2 RPC
await buildSignSubmit("/transaction-builder/open-position", openReq, [owner], V2_RPC_URL);
// Funds op → Solana RPC
await buildSignSubmit("/transaction-builder/deposit", depositReq, [owner], SOLANA_RPC_URL);
```

## Who signs

* **Owner** signs almost everything.
* **Withdrawals** (`withdraw`, `request-withdrawal`) also need a **fee payer that differs from `owner`** — the delegation program rejects `owner == feePayer`. The client holds that keypair and co-signs. See [Withdraw funds](/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/guides/withdraw-funds.md).

## Preview-only mode

`open-position` returns its quote without a transaction when you omit `owner` (`transactionBase64: null`). The [`preview/*`](/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/reference/previews.md) endpoints compute fees, exit fees, TP/SL PnL, and margin changes without building a transaction at all.

## Two error surfaces

Always check both — see [Errors](/flash-trade/flash-trade-protocol/build-on-flash/flash-trade-v2/errors.md):

* **HTTP** failures return `{ "error": "…" }` (e.g. `400` invalid pubkey, `404` unknown market/symbol).
* **Compute** failures on quote endpoints come back `200` with `{ "err": "…" }` in the body.

## Blockhash expiry

Built transactions embed a recent blockhash that expires in \~45s. On "Blockhash not found / expired," re-call the builder for a fresh transaction and submit immediately. Trading endpoints refresh the blockhash between calls so back-to-back builds don't collide.


---

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