Low wallet balance notifier

Manually tracking wallet balances in decentralized apps can mean missed alerts and failed transactions. In this guide, we’ll build a low-balance notifier that automatically sends a Telegram alert when a wallet’s native token balance falls below a chosen threshold using Kwala’s low-code automation platform. With Kwala, you can create event-driven workflows using simple YAML scripts, no backend servers required.

Objective

This guide helps you set up an automation that:

Monitors a wallet balance on the Polygon Amoy testnet.
Emits an event when the balance is below 0.1 POL.
Sends an instant Telegram alert to the user.

Prerequisites

Make sure you have:

A MetaMask wallet connected to the Polygon Amoy Testnet and Kwala network.
Remix IDE to deploy the Solidity smart contract.
A Telegram bot created via @BotFather.
Access to the Kwala Dashboard to set up the workflow.

Step 1: Build and deploy the Solidity smart contract

This Solidity contract checks user balances and emits an event when the balance drops below 0.1 POL. Solidity smart contract:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

/// @title Native POL balance checker (Polygon)
/// @notice Emits an event if a user's native POL balance is below 0.1 POL.
contract PolNativeBalanceChecker {
    // 1 POL == 1 ether in EVM units; 0.1 POL is 0.1 ether.
    uint256 public constant THRESHOLD = 0.1 ether;

    event LowPolBalance(address indexed user, uint256 balanceWei);

    /// @notice Read-only helper to get any address's native POL balance.
    function polBalanceOf(address user) public view returns (uint256) {
        return user.balance; // Wei
    }

    /// @notice Checks `user` balance and emits LowPolBalance if below 0.1 POL.
    /// @return balanceWei The user's current balance in wei.
    function checkAndWarn(address user) public returns (uint256 balanceWei) {
        balanceWei = user.balance;
        if (balanceWei < THRESHOLD) {
            emit LowPolBalance(user, balanceWei);
        }
    }

    /// @notice Convenience for the caller; checks your own balance and may emit.
    function checkMe() external returns (uint256) {
        return checkAndWarn(msg.sender);
    }
}

How it works The contract compares a user’s balance with the defined threshold. If the balance is below the threshold, it emits a LowPolBalance event: this event becomes the trigger for your Kwala workflow.

Deploy the contract using Remix and connect your MetaMask wallet to Polygon Amoy Testnet. You must have POL Faucet to deploy the smart contract.

After deployment, copy your deployed smart contract address from the Amoy Polygon explorer (https://amoy.polygonscan.com/) to inspect the contract and its transactions.

Step 2: Configure the Telegram bot

Before building the Kwala workflow, set up your Telegram bot:

Open Telegram and search @BotFather.
Run /newbot to create a bot and get a bot token.
Use @userinfobot to obtain your chat ID.

Note both:

Bot token to access the HTTP API, for example, 7754368882:AAHS4KbbOkl5rEHoBBIR8eljgwq2PARYLyY
Chat ID, for example, 968602918

Use these credentials inside the workflow to send notifications later.

Test your bot token using an API tool like ReqBin or Postman with a POST request. If the token works, the test request will deliver a Telegram notification.

Step 3: Build the workflow in Kwala

Navigate to your Kwala dashboard.
Select “Create New Workflow”.
Give your workflow a name. For example, LowBalanceNotifier1.

Workflow configuration

Triggers This is the event that activates your workflow.

Execute After: Set to event: executes the action after the event is emitted.
Repeat Every: event triggered by the event.
Expires: Add an expiration timestamp. For example, 17-09-2025 16:00 in IST.
ParameterValue: RecurringSource Contract: 0x1C5a23Fd1F7fEd9A5d020858BD4b93e5c93C92a8 the deployed smart contract address, available on Amoy Polygonscan.
Trigger Chain ID: 80002 Polygon Amoy Testnet
Recurring Event Name: LowPolBalance(address, uint256)
Event Filter: NA
Smart contract (optional): You can paste the Solidity code or upload the .sol file.
Recurring source contract ABI: Automatically fetched from the deployed contract.

Actions Next, configure the action - a Telegram notification that executes when the event occurs.

Action Name: for example, telegram_notifier
Action Type: POST API CALL
API Endpoint: https://api.telegram.org/bot<YOUR_BOT>/sendMessage
API Payload (JSON):

{
  "chat_id": 968602918,
  "text": "Low Balance! Recharge your wallet. Add 5 POL."
}

Retries Until Success: 5
Execution Mode: Sequential actions run in order

This workflow listens for the LowPolBalance event and triggers the action whenever it’s emitted.

Step 4: Add the YAML configuration

Below is the YAML script to use for your Kwala workflow. Save and compile this code in the Kwala dashboard.

Name: LowBalanceNotification15
Trigger:
  TriggerSourceContract: 0x1C5a23Fd1F7fEd9A5d020858BD4b93e5c93C92a8
  TriggerChainID: 80002
  TriggerEventName: LowPolBalance(address,uint256)
  TriggerEventFilter: NA
  TriggerSourceContractABI: 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
  TriggerPrice: NA
  RecurringSourceContract: 0x1C5a23Fd1F7fEd9A5d020858BD4b93e5c93C92a8
  RecurringChainID: 80002
  RecurringEventName: LowPolBalance(address,uint256)
  RecurringEventFilter: NA
  RecurringSourceContractABI: 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
  RecurringPrice: NA
  RepeatEvery: event
  ExecuteAfter: event
  ExpiresIn: 1789749000
  Meta: NA
  ActionStatusNotificationPOSTURL: 
  ActionStatusNotificationAPIKey: NA
Actions:
  - Name: telegram_notifier
    Type: post
    APIEndpoint: https://api.telegram.org/bot7754368882:AAHS4KbbOkl5rEHoBBIR8eljgwq2PARYLyY/sendMessage
    APIPayload:
      chat_id: '968602918'
      text: LOW BALANCE! Recharge your wallet. Add 5 POL
    TargetContract: NA
    TargetFunction: NA
    TargetParams: 
    ChainID: NA
    EncodedABI: NA
    Bytecode: NA
    EncodedGoContract: NA
    Metadata: NA
    RetriesUntilSuccess: 5
Execution:
  Mode: sequential

After successful compilation, deploy the workflow. Activate it in Kwala and wait for the workflow status to show claimed.

Make sure you are in the Kwala network (not Polygon Amoy testnet) in MetaMask when creating/deploying this workflow.

Step 5: Create a polling workflow (Optional)

You can also create a polling workflow that calls the contract on a schedule. Workflow name: for example, Polling1 Trigger

Execute After: immediate — executes the action
Repeat Every: Time interval (actions repeat on a schedule)
Expires: for example, 17-09-2025 16:00 in IST
Recurring source value configurationInterval value: time interval you want (for example, 1 in unit Min/hour/days)
Action status Notification POST URL: add the workflow’s notification URL

Actions Add the action, a smart contract call.

Action Name: for example, Polling1
Action Type: CALL (Smart Contract)
Target Function: function checkAndWarn(address user)
Target Smart contract: 0x1C5a23Fd1F7fEd9A5d020858BD4b93e5c93C92a8 (deployed contract address)
Trigger Chain ID: 80002 (Polygon Amoy Testnet)

Request body example:

{
  "chat_id": 968602918,
  "text": "Low Balance! Recharge your wallet. Add 5 POL."
}

Provide the wallet address that has Polygon Amoy testnet faucet tokens when calling the function.

Add the YAML configuration for polling

Name: Polling1
Trigger:
  TriggerSourceContract: NA
  TriggerChainID: NA
  TriggerEventName: NA
  TriggerEventFilter: NA
  TriggerSourceContractABI: NA
  TriggerPrice: NA
  RecurringSourceContract: NA
  RecurringChainID: NA
  RecurringEventName: NA
  RecurringEventFilter: NA
  RecurringSourceContractABI: NA
  RecurringPrice: NA
  RepeatEvery: 1m
  ExecuteAfter: immediate
  ExpiresIn: 1789732800
  Meta: NA
  ActionStatusNotificationPOSTURL: 
  ActionStatusNotificationAPIKey: NA
Actions:
  - Name: Polling1
    Type: call
    APIEndpoint: NA
    APIPayload:
      Message: NA
    TargetContract: 0x0F0C0b9683180DF0a13Fc176aFFd92E1F7f380f0
    TargetFunction: function checkAndWarn(address user)
    TargetParams:
      - 0x0F0C0b9683180DF0a13Fc176aFFd92E1F7f380f0
    ChainID: 80002
    EncodedABI: NA
    Bytecode: NA
    EncodedGoContract: NA
    Metadata: NA
    RetriesUntilSuccess: 5
Execution:
  Mode: parallel

Save, compile, and deploy this workflow. Activate it and wait for the workflow status to show claimed.

How it works

The trigger monitors the LowPolBalance event, and when the event fires, the workflow sends a POST request to your Telegram bot API endpoint with a custom message. Within seconds, you’ll receive a Telegram message automatically. The second automated Kwala workflow (polling) runs every minute after checkAndWarn is called in Remix; it will trigger a notification each minute. Your Telegram will display: “LOW BALANCE! Recharge your wallet. Add 5 POL” repeatedly, every minute. The process runs automatically with no manual checks required.

Test the workflow

Ensure your wallet balance is below 0.1 POL.
In Remix, call checkAndWarn(address user).
When the balance condition is met, the event is emitted, and Kwala’s nodes detect it.
Kwala executes the Telegram notification instantly.

You’ll receive: “LOW BALANCE! Recharge your wallet. Add 5 POL.” every minute (as the polling workflow repeats).

Conclusion

In this guide, you built a real-time wallet balance notifier using Kwala’s low-code workflow automation. The notifier has no backend servers or infrastructure overhead; just a smart contract and a YAML configuration. Kwala empowers developers to create, automate, and scale on-chain logic effortlessly.

Overview

Getting started

Use the Workflow Builder

Use cases

Concepts

Reference

Resources

Objective

Prerequisites

Step 1: Build and deploy the Solidity smart contract

Step 2: Configure the Telegram bot

Step 3: Build the workflow in Kwala

Workflow configuration

Step 4: Add the YAML configuration

Step 5: Create a polling workflow (Optional)

Add the YAML configuration for polling

How it works

Test the workflow

Conclusion

Next steps

Monitor Your Workflows

Best Practices

​Objective

​Prerequisites

​Step 1: Build and deploy the Solidity smart contract

​Step 2: Configure the Telegram bot

​Step 3: Build the workflow in Kwala

​Workflow configuration

​Step 4: Add the YAML configuration

​Step 5: Create a polling workflow (Optional)

​Add the YAML configuration for polling

​How it works

​Test the workflow

​Conclusion

​Next steps

Monitor Your Workflows

Best Practices

Objective

Prerequisites

Step 1: Build and deploy the Solidity smart contract

Step 2: Configure the Telegram bot

Step 3: Build the workflow in Kwala

Workflow configuration

Step 4: Add the YAML configuration

Step 5: Create a polling workflow (Optional)

Add the YAML configuration for polling

How it works

Test the workflow

Conclusion

Next steps