smoothsend-gasless

TypeScript SDK: SmoothSend Gasless Transactions

Purpose

Guide gasless transaction sponsorship on Aptos using SmoothSend. 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 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.

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Method 1: Wallet Adapter (Recommended — Any Transaction)

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

Installation

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

Provider Setup (3 lines)

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>
  );
}