> For the complete documentation index, see [llms.txt](https://docs.rallyprotocol.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rallyprotocol.com/flutter/gasless-transactions/transact-with-a-contract-gaslessly.md).

# Transact with a contract gaslessly

{% hint style="info" %}
An API key is required to use the infrastructure to power gasless transactions. Visit  <https://app.rallyprotocol.com/> to generate both Amoy and Mainnet Polygon API keys.&#x20;
{% endhint %}

## Contract requirements &#x20;

1. **Contract is compatible with the RallyMobile SDK**
   1. Contracts that are [ERC2771 compatible](/flutter/gasless-transactions/guides/add-erc2771recipient.md#if-you-are-able-to-update-the-contract) are natively supported by the RallyMobile SDK. Those that are not ERC2771 compatible must be whitelisted by us, [view the guide here.](/flutter/gasless-transactions/guides/add-erc2771recipient.md#if-you-are-able-to-update-the-contract)

## Transact with contracts with the relay method

To gaslessly execute a transaction with a contract, create a [GSN transaction object](https://github.com/rally-dfs/rly-network-mobile-sdk/blob/736e1de0859bec5230abba80e978f76f43fe2123/src/gsnClient/utils.ts#L16) and use the `relay()` method to send the transaction to our relayer.

```dart
final gsnTx = GsnTransactionDetails(
    from: accountAddress,
    data: tx.data,
    value: "0",
    to: contractAddress,
    gas: gas.toString(),
    maxFeePerGas: maxFeePerGas.toString(),
    maxPriorityFeePerGas: maxPriorityFeePerGas.toString(),
    );

await amoy.relay(gsnTx)


// relay arbitrary tx through our gasless relayer. see complete example at
// https://github.com/rally-dfs/flutter-example-app/tree/main/app/lib/services/nft.dart
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

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

```
GET https://docs.rallyprotocol.com/flutter/gasless-transactions/transact-with-a-contract-gaslessly.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

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.