Biconomy SDK (Mexa), enables meta transactions or gasless transactions in your DApp (Decentralized Application) out of the box without any change in your smart contracts and just a few lines of code in your DApp to integrate mexa.

By using Mexa, dapp users are able to use the dapp and send transactions free of cost while developer pays the gas fee on their behalf as a part of user acquisition cost.

1. Go to Mexa Dashboard to register your DApp and methods on which to enable meta transactions and copy your DApp ID and API Key.
2. Install Biconomy SDK (Mexa)

npm install @biconomy/mexa

import Biconomy from "@biconomy/mexa";
const biconomy = new Biconomy(<web3 provider>,{dappId: <DApp ID>, apiKey: <API Key>});
web3 = new Web3(biconomy);

Note: <web3 provider> could be window.ethereum for Metamask or portis.provider for Portis and so on.

biconomy.onEvent(biconomy.READY, () => {
 // Initialize your dapp here
}).onEvent(biconomy.ERROR, (error, message) => {
 // Handle error while initializing mexa
});

Congratulations!! You have now enabled meta transactions in your DApp. Interact with web3 the way you have been doing it.

Now whenever there is a write transaction action initiated from user (registered in mexa dashboard also), mexa will ask for user’s signature and handle the transaction rather than sending signed transaction directly to blockchain from user’s wallet.

Biconomy uses Contract Wallet to relay the user’s transaction to your dapp smart contract so msg.sender in your smart contracts will be user contract wallet address, so user first needs to login to biconomy to use meta transactions. We just need users signature and public address to login.

Mexa exposes a login method to let your users login to biconomy to have their contract wallet created if user comes for the first time or just return existing contract wallet address for existing users.

biconomy.login(<public wallet address>, (error, response) => {
 if(error) {
 // Error while user login to biconomy
 return;
 }

 if(response.transactionHash) {
 // First time user. Contract wallet transaction pending. Wait for confirmation.
 } else if(response.userContract) {
 // Existing user login successful
 }
});

When user login for the first time, you’ll get the transaction hash for user’s contract wallet creation transaction. On transaction confirmation mexa will emit a confirmation event.

biconomy.onEvent(biconomy.LOGIN_CONFIRMATION, (log) => {
 // User's Contract Wallet creation successful
});

Biconomy constructor takes 2 parameters

const biconomy = new Biconomy(<existing web3 provider>, options);

object required

Any web3 provider that supports personal_sign, eth_accounts, eth_sendTransaction, eth_call RPC methods and web3 subscriptions.

For example, it can be window.ethereum for Metamask or portis.provider for Portis and so on.

object required

A json object having configuration values for initializing mexa sdk.

For metamask biconomy initialization code would look like:

let options = {
 dappId: <DAPP ID>,
 apiKey: <API KEY>,
 strictMode: true
};
const biconomy = new Biconomy(window.ethereum, options);