Sign message lets you create an EIP-191. You should verify the signature. Use Case: This command is useful for applications that need to sign messages for verification purposes, ensuring that the message was indeed created by the owner of the wallet. Example: A voting app that requires users to sign a message to prove ownership of their wallet before allowing them to vote.

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Using the command

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Sending the command & handling the response

The response will include a signature compliant with EIP-191. You should verify the signature.
type MiniAppSignMessageSuccessPayload = {
  status: "success";
  signature: string;
  address: string;
  version: number;
};
app/page.tsx
import { MiniKit, SignMessageInput } from '@worldcoin/minikit-js'

const signAndVerifyMessage = async () => {
  const signMessagePayload: SignMessageInput = {
    message: "Hello world",
  };

  const {finalPayload} = await MiniKit.commandsAsync.signMessage(signMessagePayload);

  if (finalPayload.status === "success") {
    const messageHash = hashSafeMessage(messageToSign);

    const isValid = await (
      await Safe.init({
        provider:
          "https://worldchain-mainnet.g.alchemy.com/v2/your-api-key",
        safeAddress: finalPayload.address,
      })
    ).isValidSignature(messageHash, finalPayload.signature);

    // Checks functionally if the signature is correct
    if (isValid) {
      console.log("Signature is valid");
    }
  }
};
Your message is verified!