> For the complete documentation index, see [llms.txt](https://docs.vebetterdao.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.vebetterdao.org/developer-guides/reward-distribution/solidity.md).

# Solidity

In this example, we assume that you are building a smart contract where users can submit some sustainable action that is being approved/rejected by some moderator. If the action is approved the user can claim his rewards. No backend is involved.

Your contract should look like this:

<pre class="language-solidity"><code class="lang-solidity"><strong>// SPDX-License-Identifier: MIT
</strong>pragma solidity 0.8.20;

// can find here: https://github.com/vechain/vebetterdao-contracts/tree/main/contracts/interfaces
import "./interfaces/IX2EarnRewardsPool.sol";

/**
 * Example contract with key functionality to interact with the x2Earn rewards pool
 * and distribute rewards.
 * You can customize this contract in the way 
 */
contract MySustainableAppContract {
    IX2EarnRewardsPool public x2EarnRewardsPool;
    bytes32 public VBD_APP_ID;
    
    // a dummy mapping pretending you have a way to track and 
    // validate user actions on chain.
    mapping(uint256 actionId => ActionStruct) public sustainableActions;
    mapping(uint256 actionId => bool) public rewardsClaimed;
    
    // You will need to setup the address of the X2EarnRewardsPool contract
    // and your APP_ID on VeBetterDAO
    constructor(IX2EarnRewardsPool _x2EarnRewardsPool, bytes32 _VBD_APP_ID) {
        x2EarnRewardsPool = _x2EarnRewardsPool;
        VBD_APP_ID = _VBD_APP_ID;
    }

    /**
     * @notice A function that allows a user to claim a reward for a specific
     * sustainable action that they performed.
     * 
     * IMPORTANT: the address of this contract must be set as a distributor 
     * of your APP in order to move funds from the X2EarnRewardsPool contract. 
     * You can set this on the VeBetterDAO governance app.
     */
    function claimReward(uint256 _actionId) external {
        // ... some code to check if the action is valid and user can claim

        // If distributeReward fails, it will revert
        x2EarnRewardsPool.distributeReward(
            VBD_APP_ID,
            actions[_actionId].rewardAmount,
            msg.sender, // this is the user calling the claimReward function
            "" // proof and impacts not provided
        );

        rewardClaimed[_actionId] = true;

        emit RewardClaimed(_actionId, msg.sender);
    }
}
</code></pre>

### Attributing Actions to a Specific Round

If your app allows users to accumulate actions and claim later, use `distributeRewardForRound` to attribute the action to the round it was performed in:

```solidity

    function claimReward(uint256 _actionId, uint256 _actionRound) external {
        // ... some code to check if the action is valid and user can claim

        // Attribute the action to the round it was performed in
        x2EarnRewardsPool.distributeRewardForRound(
            VBD_APP_ID,
            actions[_actionId].rewardAmount,
            msg.sender,
            "",
            _actionRound // the round when the action was actually performed
        );

        rewardClaimed[_actionId] = true;

        emit RewardClaimed(_actionId, msg.sender);
    }
```

{% hint style="warning" %}
The address of this contract must be set as a **distributor** of your APP in order to move funds from the X2EarnRewardsPool contract.

You can set this on the VeBetter governance app.

<img src="/files/BexwKB5hdyLXQ5rK4d1p" alt="" data-size="original">
{% endhint %}

{% hint style="info" %}

#### Sustainability Proof

Read more about the proof standard and how we expect you to provide it in the [Sustainability Proofs and Impacts](/developer-guides/sustainability-proof-and-impacts.md) section.
{% endhint %}

{% hint style="danger" %}
To be able to distribute the rewards you will need to add the PUBLIC ADDRESS of the wallet calling the `distributeRewards` function as a Reward Distributor of your app.\
\
To do so, you need to:

1\) Connect with your app's admin wallet to the governance dapp

2\) Go to your app's page

3\) Click the *cogs* button to enter the settings page

4\) Scroll down to the "Reward Distributors" section, and add the public address as a reward distributor

5\) Save changes
{% endhint %}

<figure><img src="/files/sm9Zfrk775VqbwzT1V4R" alt=""><figcaption></figcaption></figure>


---

# 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.vebetterdao.org/developer-guides/reward-distribution/solidity.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.