Signing the transaction

const types = {
  Cast: [
    { name: "params", type: "CastParams" },
    { name: "forwardParams", type: "CastForwardParams" },
  ],
  CastParams: [
    { name: "actions", type: "Action[]" },
    { name: "id", type: "uint256" },
    { name: "avoNonce", type: "int256" },
    { name: "salt", type: "bytes32" },
    { name: "source", type: "address" },
    { name: "metadata", type: "bytes" },
  ],
  Action: [
    { name: "target", type: "address" },
    { name: "data", type: "bytes" },
    { name: "value", type: "uint256" },
    { name: "operation", type: "uint256" },
  ],
  CastForwardParams: [
    { name: "gas", type: "uint256" },
    { name: "gasPrice", type: "uint256" },
    { name: "validAfter", type: "uint256" },
    { name: "validUntil", type: "uint256" },
    { name: "value", type: "uint256" },
  ],
};

const avocadoRPCChainId = "634";
const chainId = (await polygonProvider.getNetwork()).chainId; // e.g. when executing later on Polygon

const domain = {
  name: domainName, // see previous steps
  version: domainVersion, // see previous steps
  chainId: avocadoRPCChainId,
  verifyingContract: avocadoAddress, // see previous steps
  salt: ethers.utils.solidityKeccak256(["uint256"], [chainId]), // salt is set to actual chain id where execution happens
};

// make sure you are on chain id 634 (to interact with Avocado RPC)
const avoSigner = provider.getSigner();

// sign transaction payload as built in previous step
const signature = await avoSigner._signTypedData(domain, types, txPayload);