> ## Documentation Index
> Fetch the complete documentation index at: https://docs.x402.org/llms.txt
> Use this file to discover all available pages before exploring further.

# ERC-20 Approval Gas Sponsoring

> Gasless Permit2 approval for any ERC-20 token, including those without EIP-2612. The facilitator sponsors the gas for the approval transaction.

The ERC-20 approval gas sponsoring extension enables gasless Permit2 approval for **any ERC-20 token**, including those that do not implement EIP-2612. The client signs (but does not broadcast) a standard `approve(Permit2, MaxUint256)` transaction, and the facilitator broadcasts it atomically before settling the Permit2 payment.

## Overview

This is the universal fallback for gasless Permit2 onboarding. While [EIP-2612 gas sponsoring](/extensions/eip2612-gas-sponsoring) is preferred for tokens that support it, this extension works with every ERC-20 token:

* **For Buyers**: No gas needed — sign an approval transaction off-chain and the facilitator broadcasts it
* **For Sellers**: Advertise this extension to support the widest range of ERC-20 tokens
* **For Facilitators**: Broadcast the pre-signed approval and settle in an atomic batch, optionally funding the client's gas if needed

## How It Works

1. **Server** advertises `erc20ApprovalGasSponsoring` in the `PaymentRequired` response extensions
2. **Client** checks if Permit2 allowance is insufficient; if so, signs a raw `approve(Permit2, MaxUint256)` transaction without broadcasting it
3. **Client** includes the signed transaction in `extensions.erc20ApprovalGasSponsoring.info.signedTransaction`
4. **Facilitator** executes an atomic batch:
   * Funds the client's wallet with gas (if needed)
   * Broadcasts the client's signed approval transaction
   * Calls `x402ExactPermit2Proxy.settle()` to complete the payment

The atomic batch ensures the approval and settlement happen together — there is no window for front-running between the approval and the payment.

## Server Usage

Advertise support for this extension in your route configuration:

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    import { declareErc20ApprovalGasSponsoringExtension } from "@x402/extensions/erc20-approval-gas-sponsoring";

    const routes = {
      "GET /api/data": {
        accepts: [{
          scheme: "exact",
          network: "eip155:84532",
          price: "$0.01",
          payTo: "0xYourAddress",
        }],
        extensions: {
          ...declareErc20ApprovalGasSponsoringExtension(),
        },
      },
    };
    ```
  </Tab>

  <Tab title="Go">
    ```go theme={null}
    import (
        "github.com/x402-foundation/x402/go/extensions/erc20approvalgassponsor"
    )

    extensions := erc20approvalgassponsor.DeclareExtension()
    // Include in your route's Extensions field
    ```
  </Tab>

  <Tab title="Python">
    ```python theme={null}
    from x402.extensions.erc20_approval_gas_sponsoring import (
        declare_erc20_approval_gas_sponsoring_extension,
    )

    routes = {
        "GET /api/data": {
            "accepts": {
                "scheme": "exact",
                "network": "eip155:84532",
                "price": "$0.01",
                "payTo": "0xYourAddress",
            },
            "extensions": {
                **declare_erc20_approval_gas_sponsoring_extension(),
            },
        },
    }
    ```
  </Tab>
</Tabs>

## Client Usage

The `ExactEvmScheme` handles ERC-20 approval gas sponsoring automatically as a fallback when EIP-2612 is not available.

<Tabs>
  <Tab title="TypeScript">
    ```typescript theme={null}
    import { ExactEvmScheme } from "@x402/evm/exact/client";

    // signTransaction and getTransactionCount capabilities are required
    const scheme = new ExactEvmScheme(signer);
    client.register("eip155:*", scheme);

    // The scheme automatically signs an ERC-20 approval when:
    // 1. The server advertises erc20ApprovalGasSponsoring
    // 2. The asset transfer method is "permit2"
    // 3. The client's Permit2 allowance is insufficient
    // 4. EIP-2612 gas sponsoring is not available or not supported by the token
    ```
  </Tab>

  <Tab title="Go">
    ```go theme={null}
    import (
        evm "github.com/x402-foundation/x402/go/mechanisms/evm/exact/client"
    )

    scheme := evm.NewExactEvmScheme(signer)
    client.Register("eip155:*", scheme)

    // ERC-20 approval gas sponsoring is handled automatically
    // as a fallback when EIP-2612 is not available
    ```
  </Tab>

  <Tab title="Python">
    ```python theme={null}
    from x402 import x402Client
    from x402.mechanisms.evm import EthAccountSignerWithRPC
    from x402.mechanisms.evm.exact import register_exact_evm_client

    account = Account.from_key("0xYourPrivateKey")
    signer = EthAccountSignerWithRPC(account, rpc_url="https://sepolia.base.org")

    client = x402Client()
    register_exact_evm_client(client, signer)
    # Automatically signs ERC-20 approval transaction when needed
    ```
  </Tab>
</Tabs>

## When to Use

Use this extension when:

* You want to support any ERC-20 token, not just those with EIP-2612
* You're using the `permit2` asset transfer method
* You want fully gasless onboarding for your users regardless of the token

This extension is typically advertised alongside [EIP-2612 gas sponsoring](/extensions/eip2612-gas-sponsoring). The client automatically selects the best option: EIP-2612 if the token supports it, ERC-20 approval otherwise.

## SDK Support

| SDK        | Supported |
| ---------- | --------- |
| TypeScript | ✅         |
| Go         | ✅         |
| Python     | ✅         |