Step 2: Prepare Payload

Once you've managed with Rule ID, now you are ready to prepare a payload

The payload must be a valid typed structured json according to EIP-712

There is an example how to prepare it using Viem and PureFi Verifier-SDK npm packages in Typescript, but feel free to make your own implementation

import { parseUnits, createWalletClient, custom, http, Chain } from 'viem';

import {
  PureFI,
  PackageType,
  createDomain,
  createRuleV5Types,
  RuleV5Data,
  RuleV5Payload,
  PureFIRuleV5Payload,
} from '@purefi/verifier-sdk';

async function preparePayload(
  ruleId: string,
  packageType: PackageType,
  userAddress: `0x${string}`,
  contractAddress: `0x${string}`,
  token0Address: `0x${string}`, // zero address for native coins
  token0Decimals: number,
  token0Value: string,
  chain: Chain
): Promise<PureFIRuleV5Payload> {
  const domain = createDomain('PureFi', chain.id);

  const token0ValueParsed = parseUnits(token0Value, token0Decimals);

  const ruleV5Payload: RuleV5Payload = {
    ruleId,
    from: userAddress,
    to: contractAddress,
    tokenData0: {
      address: token0Address,
      value: token0ValueParsed.toString(),
      decimals: token0Decimals.toString(),
    },
    packageType,
  };

  const ruleV5Data: RuleV5Data = {
    account: {
      address: userAddress,
    },
    chain: {
      id: chain.id.toString(),
    },
    payload: ruleV5Payload,
  };

  const v5RuleTypes = createRuleV5Types(ruleV5Payload);

  // IN CASE OF BACKEND INTEGRATION, e.g. Custom Signer

  // const account = privateKeyToAccount('0x...')
  // const walletClient = createWalletClient({
  //   account,
  //   chain,
  //   transport: http(),
  // });

  const walletClient = createWalletClient({
    chain,
    transport: custom((window as any).ethereum!),
  });

  const signature = await walletClient.signTypedData({
    account: userAddress,
    domain,
    types: v5RuleTypes,
    primaryType: 'Data',
    message: ruleV5Data,
  });

  const payload: PureFIRuleV5Payload = {
    message: ruleV5Data,
    signature,
  };

  return payload;
}