Using API

Use our APIs to easily implement meta transactions!

Note:

Before using this API, make sure you have Trusted Forwarder support in your smart contracts i.e., you have removed the dependency on msg.sender property from your smart contracts and trusted forwarder is added.

/api/v2/meta-tx/native

POST https://api.biconomy.io/api/v2/meta-tx/native

Our API lets you relay transactions directly to your smart contract without your end users having to pay any transaction/gas fee. Just register your dApp on the developer dashboard, upload your smart contracts as meta transaction type as Trusted Forwarder and select your methods in which you want to enable native meta transaction support.

Headers

Name	Type	Description
x-api-key	string	API key present on your dashboard for your DApp after DApp registration. This is specific to DApp registered.

Request Body

Name	Type	Description
signatureType	string	Signature type chosen by the developer to sign the transaction message. Accepted values are EIP712_SIGN and PERSONAL_SIGN. If omitted personal signature will be assumed by the server and will expect only two parameters (signature and request) in params.
gasLimit	string	Gas limit to be set in the transaction. It can be a decimal number or hexadecimal string. If omitted web3 estimateGas method will be used to calculate the gasLimit for the transaction.
from	string	User client wallet public address who is supposed to be sending the transaction eg. metamask wallet address or portis wallet address.
params	array	Array of all the parameters required to call the execute methods of the trusted forwarder depending on the signature type. Read more about this in below section
apiId	string	API id corresponding to the method you want to call in your smart contract. It can be found on the dashboard under 'Manage APIs' section.
to	string	Target Contract Address.

200 Transaction successfully sent

 {
    "txHash": "0x84bc6f25b964f794f90c59b4f97a16aadc878ce53187703124b5e0ee52e15af9",
    "message": "Meta transaction sent to blockchain",
    "retryDuration": 158, 
    "flag": 200
}
//retryDuration: time in seconds after which you 
//can check resubmitted endpoint for new hash in case of
//potential resubmits.

404 Required data not found

409 When Limits set on dashboard are reached. Check the code field to see which limit is reached. See "Check Limit" under API section to see all possible values of code field. code = 150, when DApp limits are reached code = 151, when User limits are reached code = 152, when API per user limits are reached

417 When gas estimation is failed due to any revert on your contracts due to any business logic. Usually you'll see the revert error message in response, but to debug the issue, try sending the same transaction without Biconomy to see the actual error on the explorer.

Example Curl Request

curl 
--request POST 'https://api.biconomy.io/api/v2/meta-tx/native'  
--header 'x-api-key: <api_key_from_dashboard>'  
--header 'Content-Type: application/json'  
--data-raw '{ 
"from": "<user_public_address>",
"apiId": "<api_id_from_dashboard>", 
"params": [<param1>,<param2>,...... ],
"to": "<recipient_contract_address>",
"gasLimit":"0xF4240",
"signatureType":"EIP712Sign"
}'

If the signature type is EIP712, params are [request, domainSeperator, signature] params = [request, domainSeparator, sig];

If signature type is personal sign, (assumed default if signatureType parameter is omitted in API request body) params are [request, signature]. params = [request, sig];

Biconomy has helpers available to build above mentioned parameters from your dapp transaction.

For EIP2771, below is an example code on how to use Biconomy helpers JS to build request, domain separator and data to sign for each signature type and then send API request to the Biconomy servers where our relayer infrastructure will process your transaction.

Sample code

web3

Check the repository here for complete example code

import {
    helperAttributes,
    getDomainSeperator,
    getDataToSignForPersonalSign,
    getDataToSignForEIP712,
    buildForwardTxRequest,
    getBiconomyForwarderConfig
  } from './biconomyForwarderHelpers';
  
let sigUtil = require("eth-sig-util"); // additional dependency 

// This web3 instance is used to get user signature from connected wallet
let walletWeb3 = new Web3(window.ethereum);


let userAddress = <selected address>;
let networkId = <your provider networkId here>;

// Initialize Contracts
let contract = new web3.eth.Contract(
              <CONTRACT_ABI>,
              <CONTRACT_ADDRESS>
            );

let functionSignature = contract.methods
                  .setQuote(newQuote)
                  .encodeABI();
let txGas = await contract.methods
                  .setQuote(newQuote)
                  .estimateGas({ from: userAddress });
                  
let forwarder = await getBiconomyForwarderConfig(networkId);
let forwarderContract = new web3.eth.Contract(
          forwarder.abi,
          forwarder.address
        );

//const batchId = await forwarderContract.methods.getBatch(userAddress).call();
const batchNonce = await forwarderContract.methods.getNonce(address,0).call();
const gasLimitNum = Number(txGas);
const to = <CONTRACT_ADDRESS>;

const request = await buildForwardTxRequest({account:userAddress,to,gasLimitNum,batchId,batchNonce,data:functionSignature});

/* If you wish to use EIP712 Signature type check below code*/


const hashToSign = getDataToSignForPersonalSign(request);
const sig = await walletWeb3.eth.personal.sign("0x" + hashToSign.toString("hex"), userAddress);
sendTransaction({userAddress, request, sig, signatureType:biconomy.PERSONAL_SIGN});
// notice domain seperator is not passed here

///////////////////////////////////////////////////////////

 // If you wish to use EIP712 Signature type  
 //build the request as mentioned above
   const domainSeparator = await getDomainSeperator(42);
   console.log(domainSeparator);
   const dataToSign =  await getDataToSignForEIP712(request,networkId);
   

 walletWeb3.currentProvider.send(
                    {
                        jsonrpc: "2.0",
                        id: 999999999999,
                        method: "eth_signTypedData_v4",
                        params: [userAddress, dataToSign]
                    },
                    function (error, response) {
                        console.info(`User signature is ${response.result}`);
                        if (error || (response && response.error)) {
                            showErrorMessage("Could not get user signature");
                        } else if (response && response.result) {
                            let sig = response.result;
                            sendTransaction({userAddress, request, domainSeparator, sig, signatureType:biconomy.EIP712_SIGN});
                        }
                    }
                );
 
  

ethers

Great! Once your parameters are built you are ready to make the API call to send gasless transactions!

const sendTransaction = async ({userAddress, request, sig, domainSeparator, signatureType}) => {
        if (web3 && contract) {
          let params;
          if (domainSeparator) {
            params = [request, domainSeparator, sig];
          } else {
            params = [request, sig];
          }
          try {
            fetch(`https://api.biconomy.io/api/v2/meta-tx/native`, {
              method: "POST",
              headers: {
                "x-api-key": <YOUR_DAPP_API_KEY>,
                "Content-Type": "application/json;charset=utf-8",
              },
              body: JSON.stringify({
                to: <CONTRACT_ADDRESS>,
                apiId: <METHOD_API_ID>,
                params: params,
                from: userAddress,
                signatureType: signatureType
              }),
            })
              .then((response) => response.json())
              .then(async function (result) {
                console.log(result);
                showInfoMessage(
                  `Transaction sent by relayer with hash ${result.txHash}`
                );

                let receipt = await getTransactionReceiptMined(
                  result.txHash,
                  2000
                );
                setTransactionHash(result.txHash);
                showSuccessMessage("Transaction confirmed on chain");
                getQuoteFromNetwork();
              })
              .catch(function (error) {
                console.log(error);
              });
          } catch (error) {
            console.log(error);
          }
        }
    };
    
  ////helper///

  //for web3  
  const getTransactionReceiptMined = (txHash, interval) => {
        const self = this;
        const transactionReceiptAsync = async function(resolve, reject) {
          var receipt = await web3.eth.getTransactionReceipt(txHash);
          if (receipt == null) {
              setTimeout(
                  () => transactionReceiptAsync(resolve, reject),
                  interval ? interval : 500);
          } else {
              resolve(receipt);
          }
        };
    
        if (typeof txHash === "string") {
            return new Promise(transactionReceiptAsync);
        } else {
            throw new Error("Invalid Type: " + txHash);
        }
      };

Congratulations 👏

You're now ready to use the trusted forwarder approach and enable gasless transactions in your dApp using SDK and/or APIs. Check out other implementations and in-depth technical details in the following sections.