MiniPay Integration

This skill covers building Mini Apps for MiniPay, the fastest growing non-custodial wallet in the Global South with 10M+ activations.

When to Use

• Building Mini Apps for MiniPay
• Detecting MiniPay wallet in your dApp
• Creating mobile-first payment applications
• Integrating with MiniPay's discovery page

What is MiniPay?

MiniPay is a stablecoin wallet with a built-in Mini App discovery page. It's available as:

• Built into Opera Mini browser (Android)
• Standalone app (Android and iOS)

Key features:

• Phone number mapping to wallet addresses
• Sub-cent transaction fees
• 2MB lightweight footprint
• Supports USDm (cUSD), USDC, and USDT

Quick Start

Create a MiniPay App

npx @celo/celo-composer@latest create -t minipay

This scaffolds a Next.js app pre-configured for MiniPay.

Detecting MiniPay

Check if the user is using MiniPay:

function isMiniPay(): boolean {
  return typeof window !== "undefined" &&
         window.ethereum?.isMiniPay === true;
}

Important: This code must run in a browser environment, not Node.js.

Connecting Wallet

MiniPay automatically injects the wallet. Request account access:

async function connectWallet(): Promise<string | null> {
  if (typeof window === "undefined" || !window.ethereum) {
    return null;
  }

  const accounts = await window.ethereum.request({
    method: "eth_requestAccounts",
    params: [],
  });

  return accounts[0] || null;
}

Important: Hide the "Connect Wallet" button when inside MiniPay - the connection is implicit.

const [address, setAddress] = useState<string | null>(null);
const inMiniPay = isMiniPay();

useEffect(() => {
  if (inMiniPay) {
    connectWallet().then(setAddress);
  }
}, [inMiniPay]);

return (
  <div>
    {!inMiniPay && (
      <button onClick={() => connectWallet().then(setAddress)}>
        Connect Wallet
      </button>
    )}
    {address && <p>Connected: {address}</p>}
  </div>
);

Reading Balances

import { createPublicClient, http, formatUnits } from "viem";
import { celo } from "viem/chains";

const publicClient = createPublicClient({
  chain: celo,
  transport: http(),
});

const USDM_ADDRESS = "0x765de816845861e75a25fca122bb6898b8b1282a";

const ERC20_ABI = [
  {
    name: "balanceOf",
    type: "function",
    stateMutability: "view",
    inputs: [{ name: "account", type: "address" }],
    outputs: [{ type: "uint256" }],
  },
] as const;

async function getUSDmBalance(address: string): Promise<string> {
  const balance = await publicClient.readContract({
    address: USDM_ADDRESS,
    abi: ERC20_ABI,
    functionName: "balanceOf",
    args: [address as `0x${string}`],
  });

  return formatUnits(balance, 18);
}

Sending Transactions

Use viem or wagmi for transactions. MiniPay does not support ethers.js.

import { createWalletClient, custom, parseUnits, encodeFunctionData } from "viem";
import { celo } from "viem/chains";

const USDM_ADDRESS = "0x765de816845861e75a25fca122bb6898b8b1282a";

const ERC20_ABI = [
  {
    name: "transfer",
    type: "function",
    stateMutability: "nonpayable",
    inputs: [
      { name: "to", type: "address" },
      { name: "amount", type: "uint256" },
    ],
    outputs: [{ type: "bool" }],
  },
] as const;

async function sendUSDm(to: string, amount: string): Promise<string> {
  const walletClient = createWalletClient({
    chain: celo,
    transport: custom(window.ethereum),
  });

  const [address] = await walletClient.getAddresses();

  const hash = await walletClient.sendTransaction({
    account: address,
    to: USDM_ADDRESS,
    data: encodeFunctionData({
      abi: ERC20_ABI,
      functionName: "transfer",
      args: [to as `0x${string}`, parseUnits(amount, 18)],
    }),
  });

  return hash;
}

Testing Your Mini App

1. Set Up ngrok

MiniPay cannot access localhost. Use ngrok to create a tunnel:

ngrok http 3000

2. Enable Developer Mode in MiniPay

1. Open MiniPay > Settings > About
2. Tap Version number repeatedly until Developer Mode is enabled
3. Go to Settings > Developer Settings
4. Enable "Use Testnet" for Celo Sepolia

3. Load Your App

1. Open MiniPay > Tap compass icon
2. Select "Test Page"
3. Enter your ngrok HTTPS URL
4. Tap "Go"

Requirements and Limitations

Supported

• Celo Mainnet and Celo Sepolia Testnet only
• viem v2+ and wagmi libraries
• TypeScript v5+, Node.js v20+
• USDm (cUSD), USDC, and USDT stablecoins

Not Supported

• ethers.js (use viem instead)
• EIP-1559 transactions (legacy only)
• Message signing
• Android/iOS emulators (use real device)
• Other blockchain networks

Dependencies

{
  "dependencies": {
    "viem": "^2.0.0",
    "@celo/abis": "^11.0.0"
  },
  "devDependencies": {
    "typescript": "^5.0.0"
  }
}

Additional Resources

• testing-guide.md - Detailed testing instructions
• troubleshooting.md - Common issues and solutions
• code-examples.md - Gas estimation, fee currency, React hooks