smoothsend-gasless

by iskysun96

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SKILL.md About

---
name: smoothsend-gasless
description:
  "How to sponsor gas fees for Aptos dApp users using SmoothSend. Paid commercial service: free on testnet, credit-based
  on mainnet. Covers 3-line wallet adapter integration (transactionSubmitter), Script Composer for fee-in-token
  stablecoin transfers. Triggers on: 'gasless', 'sponsor gas', 'users pay no APT', 'transactionSubmitter', 'SmoothSend',
  'fee payer', 'pay gas for users', 'no gas required'."
metadata:
  author: ivedmohan
  version: "1.0"
  category: sdk
  tags: ["typescript", "sdk", "wallet", "gasless", "sponsored", "smoothsend", "transactionSubmitter"]
---

# TypeScript SDK: SmoothSend Gasless Transactions

## Purpose

Guide **gasless transaction sponsorship** on Aptos using [SmoothSend](https://smoothsend.xyz). Users sign transactions
via their wallet but never pay gas — you pay per transaction from pre-loaded credits. Works as a drop-in
`transactionSubmitter` for `AptosWalletAdapterProvider`.

**Paid commercial service:** Free on testnet; mainnet uses credit-based billing. See
[Pricing](https://docs.smoothsend.xyz/pricing) for current rates.

## ALWAYS

1. **Use `@smoothsend/sdk`** — official npm package for SmoothSend integration.
2. **Pass `SmoothSendTransactionSubmitter` as `transactionSubmitter`** in `AptosWalletAdapterProvider` — this enables
   gasless for all `signAndSubmitTransaction` calls.
3. **Store API key in env** — use `NEXT_PUBLIC_SMOOTHSEND_API_KEY` or `VITE_SMOOTHSEND_API_KEY` (never hardcode).
4. **Use testnet for development** — testnet is always free; no credits required.
5. **Handle 402 (Insufficient credits)** — API returns 402 when credits run out; show user-friendly message and link to
   billing.

## NEVER

1. **Do not expose API key in server-side only apps to client** — for frontend, use `NEXT_PUBLIC_` or `VITE_` prefixed
   env vars.
2. **Do not skip `transactionSubmitter`** — without it, users pay gas themselves; the provider falls back to normal
   submission.
3. **Do not use Script Composer for arbitrary transactions** — Script Composer is for stablecoin transfers (USDC, USDT,
   etc.) only; use Wallet Adapter for everything else.

---

## Method 1: Wallet Adapter (Recommended — Any Transaction)

Use for swaps, NFT mints, contract calls — any transaction type.

### Installation

```bash
npm install @smoothsend/sdk @aptos-labs/wallet-adapter-react
```

### Provider Setup (3 lines)

```tsx
import { SmoothSendTransactionSubmitter } from "@smoothsend/sdk";
import { AptosWalletAdapterProvider } from "@aptos-labs/wallet-adapter-react";
import { Network } from "@aptos-labs/ts-sdk";

const smoothSend = new SmoothSendTransactionSubmitter({
  apiKey: process.env.NEXT_PUBLIC_SMOOTHSEND_API_KEY!,
  network: "mainnet" // or 'testnet' (always free)
});

export function Providers({ children }: { children: React.ReactNode }) {
  return (
    <AptosWalletAdapterProvider
      autoConnect={true}
      dappConfig={{
        network: Network.MAINNET,
        transactionSubmitter: smoothSend
      }}
      onError={(error) => console.error("Wallet error:", error)}
    >
      {children}
    </AptosWalletAdapterProvider>
  );
}
```

After this, every `signAndSubmitTransaction` call is gasless. No other code changes needed.

---

## Method 2: Script Composer (Fee-in-Token — Stablecoin Only)

Use for USDC, USDT, WBTC, USDe, USD1 transfers. Fee (~$0.01) is deducted from the token being sent — no APT or
SmoothSend credits required.

```typescript
import { ScriptComposerClient } from "@smoothsend/sdk";

const client = new ScriptComposerClient({
  apiKey: process.env.NEXT_PUBLIC_SMOOTHSEND_API_KEY!,
  network: "mainnet"
});

// USDC Mainnet asset address
const USDC_ASSET = "0xbae207659db88bea0cbead6da0ed00aac12edcdda169e591cd41c94180b46f3b";

const build = await client.buildTransfer({
  sender: walletAddress,
  recipient: "0xRecipient...",
  amount: "1000000", // 1 USDC (6 decimals)
  assetType: USDC_ASSET,
  decimals: 6,
  symbol: "USDC"
});

// Sign with wallet, then submit build.signedTransaction
```

---

## Error Handling

```tsx
try {
  const response = await signAndSubmitTransaction(payload);
  await aptos.waitForTransaction({ transactionHash: response.hash });
} catch (error: any) {
  if (error?.status === 402 || error?.message?.includes("Insufficient credits")) {
    // Credits exhausted — show upgrade CTA
    toast.error("Service temporarily unavailable. Please try again later.");
    window.open("https://dashboard.smoothsend.xyz/billing", "_blank");
  } else {
    throw error;
  }
}
```

---

## Pricing

See [SmoothSend Pricing](https://docs.smoothsend.xyz/pricing) for current rates. Testnet is free; mainnet uses credit
packs.

---

## Common Mistakes

| Mistake                                   | Correct approach                                             |
| ----------------------------------------- | ------------------------------------------------------------ |
| Forgetting `transactionSubmitter`         | Pass `smoothSend` in `dappConfig`                            |
| Hardcoding API key                        | Use env var with `NEXT_PUBLIC_` or `VITE_` prefix            |
| Using Script Composer for non-transfer tx | Use Wallet Adapter for swaps, mints, contract calls          |
| Not handling 402                          | Catch and show user-friendly message + billing link          |
| Wrong network                             | Match `network` in SmoothSend config to `dappConfig.network` |

---

## References

- SmoothSend Docs: https://docs.smoothsend.xyz
- Pricing: https://docs.smoothsend.xyz/pricing
- Dashboard: https://dashboard.smoothsend.xyz
- npm: https://www.npmjs.com/package/@smoothsend/sdk
- MCP (AI context): `npx @smoothsend/mcp` — tools for get_docs, estimate_credits, get_code_snippet
- Related: [ts-sdk-wallet-adapter](../../skills/sdk/typescript/ts-sdk-wallet-adapter/SKILL.md),
  [ts-sdk-transactions](../../skills/sdk/typescript/ts-sdk-transactions/SKILL.md)

_meta.json Metadata

{
  "ownerId": "kn7bzgtfz4k38gc65fzse22xjn8344yr",
  "publishedAt": 1773855295074,
  "slug": "smoothsend-gasless",
  "version": "1.0.0"
}