# Paymaster Endpoint

As per [ERC-4337](https://eips.ethereum.org/EIPS/eip-4337), Paymasters facilitate transaction sponsorship, allowing third-party-designed mechanisms to pay for transactions. Many of these mechanisms *could* be done by having the paymaster wrap a `UserOperation` with their own, but there are some important fundamental limitations to that approach:

* No possibility for “passive” paymasters (eg. that accept fees in some ERC-20 token at an exchange rate pulled from an on-chain DEX)
* Paymasters run the risk of getting griefed, as users could send ops that appear to pay the paymaster but then change their behavior after a block

### Utilize the following APIs to get paymaster data and signature.

### /getpaymasterdata

## Get the paymaster data, that can be sent in the user operations.

<mark style="color:blue;">`GET`</mark> `https://api.expand.network/aa/getpaymasterdata`

#### Query Parameters

| Name                                                       | Type   | Description                                                                                                                                            |
| ---------------------------------------------------------- | ------ | ------------------------------------------------------------------------------------------------------------------------------------------------------ |
| chainId                                                    | String | Refer to the [Chain ID ](/ids/chain-ids.md)page for details.                                                                                           |
| chainSymbol                                                | String | Refer to the [Chain ID ](/ids/chain-ids.md)page for details.                                                                                           |
| sender<mark style="color:red;">\*</mark>                   | String | On-chain wallet address.                                                                                                                               |
| rpc                                                        | String | Remote procedural call URL.                                                                                                                            |
| nonce                                                      | String | Anti-replay parameter.                                                                                                                                 |
| initCode                                                   | String | The initCode of the account. (needed if and only if the account is not yet on-chain and needs to be created)                                           |
| preVerificationGas                                         | String | The amount of gas to pay for to compensate the bundler for pre-verification execution and calldata.                                                    |
| verificationGasLimit                                       | String | The amount of gas to allocate for the verification step.                                                                                               |
| gasLimit                                                   | String | Maximum gas limit provided by the sender, for the transaction.                                                                                         |
| callGasLimit                                               | String | The amount of gas to allocate the main execution call.                                                                                                 |
| callData                                                   | String | Encoded data for executing the primary function call or operation within the user's transaction.                                                       |
| maxPriorityFeePerGas                                       | String | Maximum priority fee per gas. (similar to EIP-1559 `max_priority_fee_per_gas`)                                                                         |
| maxFeePerGas                                               | String | The maximum fee per gas to pay for the execution of this operation. (similar to [EIP-1559](https://eips.ethereum.org/EIPS/eip-1559) `max_fee_per_gas`) |
| signature                                                  | String | Data passed into the account along with the nonce during the verification step.                                                                        |
| paymasterAndData                                           | String | Address of paymaster sponsoring the transaction, followed by extra data to send to the paymaster. (empty for self-sponsored transaction)               |
| paymasterContractAddress<mark style="color:red;">\*</mark> | String | Address of the contract from where, gas is to be paid.                                                                                                 |
| mockValidAfter<mark style="color:red;">\*</mark>           | String | The UserOp is valid only after this time, to be sent in epoch time format.                                                                             |
| mockValidUntil<mark style="color:red;">\*</mark>           | String | The UserOp is valid only up to this time, to be sent in epoch time format.                                                                             |

{% tabs %}
{% tab title="Sample Request" %}

```url
https://api.expand.network/aa/getpaymasterdata?sender=0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&chainId=1&paymasterContractAddress=0xba60b04029be2bfd16d76e70290acfad3a8b582c&mockValidUntil=0x00000000deadbeef&mockValidAfter=0x0
```

{% endtab %}

{% tab title="Sample Response" %}

```json
{
    "status": 200,
    "msg": "success",
    "data": {
        "paymasterData": "0xba60b04029be2bfd16d76e70290acfad3a8b582c00000000000000000000000000000000000000000000000000000000deadbeef00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
        "hash": "0x2907ffb2f2320e35a041bd74235caed02f706e3ed4b2308f0a064a1f9e0aac67",
        "mockValidUntil": "0x00000000deadbeef",
        "mockValidAfter": "0x0"
    }
}
```

{% endtab %}
{% endtabs %}


---

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Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
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```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.