Metamask 0x API: Invalid Signature - A Guide to Successful EIP-721 and EIP-1155 Transactions

As a Metamask user, you're likely aware of the various APIs that allow you to interact with the Ethereum blockchain. In this article, we'll focus on two specific APIs: 0x for EIP-721 (Non-Fungible Token) transactions, including approval and signing of contracts, and 0x for EIP-1155 (ERC-20 token) transactions.

Understanding EIP-721

EIP-721 is a specification for creating non-fungible tokens on the Ethereum blockchain. These tokens can represent unique assets such as art, collectibles, or in-game items. To create these tokens, you need to deploy them on the Ethereum network using smart contracts. One common way to deploy EIP-721 tokens is through the use of the 0x API.

EIP-1155 and ERC-20 Tokens

ERC-20 (Ethereum-based Standard) tokens are a type of fungible token, meaning that they can be bought, sold, and traded like any other asset. One common way to deploy ERC-20 tokens is through the use of the 0x API.

Signing Approval with Metamask 0x

When signing an approval contract in Metamask 0x, you need to provide a valid signature that proves your identity and confirms your authority over the contract's smart contract. To do this, follow these steps:

• 
  Deploy the Approval Contract: Deploy an EIP-721 or ERC-20 token contract on the Ethereum network.

• 
  Create a MetaMask App
  
  
  
  
  
  
  
  
  : Create a new application in Metamask 0x and add the deployed contract to it.

• 
  Configure Signatures: In your application, configure the signers property of the contract with your MetaMask private key.

• 
  Sign Approval: Call the approve function on the contract using your signed private key.

Here's an example code snippet in Solidity (the programming language used for smart contracts):

pragma solidity ^0.8.0;


contract MyApproval {

    mapping(address => uint256) public approved;


    function approve(address owner, uint256 value) public payable {

        require(!approved[owner], "Already approved");

        approved[owner] = value;

    }


    function getApproved() public view returns (uint256) {

        return approved[msg.sender];

    }

}

Invalid Signature Error

If you try to sign an approval contract using an invalid signature, Metamask 0x will throw an error. This is because the signers property of the contract needs to be configured with a valid private key.

To resolve this issue, ensure that you have properly configured your MetaMask private key for signing approvals in your application. Here are some steps to follow:

• 
  Export Your Private Key: Export your private key as a JSON Web Key (JWK) or an Ethereum wallet-compatible public-private key.

• 
  Configure Signers in Your App: In your application, configure the signers property of the contract with your exported private key.

Example code snippet:

pragma solidity ^0.8.0;


contract MyApproval {

    mapping(address => uint256) public approved;

    mapping(address => string) public signer;


    function approve(address owner, uint256 value) public payable {

        require(!signer[msg.sender], "Invalid signature");

        signer[msg.sender] = keccak256(abi.encodePacked(msg.sender, address(this), value));

    }


    function getApproved() public view returns (uint256) {

        return approved[msg.sender];

    }

}

Best Practices

To avoid invalid signature errors in the future:

• Always export your private key as a JSON Web Key or an Ethereum wallet-compatible public-private key.

• Ensure that you're using the correct signers property configuration for each contract deployment.

• Test your signing process thoroughly to ensure it works correctly.