Metamask 0x API: Invalid Signature – A Guide to Successful EIP-721 and EIP-1155 Transactions
As a Metamask user, you are probably familiar with the different APIs that allow you to interact with the Ethereum blockchain. In this article, we will focus on two specific APIs: 0x for EIP-721 (non-fungible token) transactions, including contract approval and signing, and 0x for EIP-1155 (ERC-20 token) transactions.
Understanding the EIP-721 Standard
EIP-721 is a specification for creating non-fungible tokens on the Ethereum blockchain. These tokens can represent unique assets such as artwork, collectibles, or in-game items. To create these tokens, you must deploy them to the Ethereum network using smart contracts. A common way to deploy EIP-721 tokens is to use the 0x API.
EIP-1155 and ERC-20 Tokens
ERC-20 tokens (an Ethereum-based standard) are a type of fungible token, meaning they can be bought, sold, and traded like any other asset. A common way to deploy ERC-20 tokens is to use the 0x API.
Approval Signing with Metamask 0x
When signing an approval contract in Metamask 0x, you must 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 to the Ethereum network.
- Create a MetaMask application: 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.
- Signal Approval: Call the « approve » function on the contract using your signed private key.
Here is an example code snippet in Solidity (the programming language used for smart contracts):
pragma solidity ^0.8.0;
contract MyApproval {
map(address => uint256) public approved;
function approve(address owner, value uint256) public payable {
require(!approved[owner], "Already approved");
approved[owner] = value;
}
function getApproved() public view return (uint256) {
return approved[msg.sender];
}
}
Invalid Signature Error
If you try to sign an endorsement contract using an invalid signature, Metamask 0x will throw an error. This is because the « signatories » property of the contract must be configured with a valid private key.
To resolve this issue, make sure you have properly configured your MetaMask private key to sign endorsements 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 application: In your application, configure the « signatories » 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, value uint256) public payable {
require(!signer[msg.sender], "Invalid signature");
signer[msg.sender] = keccak256(abi.encodePacked(msg.sender, address(this), value));
}
function getApproved() public view return (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 are using the correct « signers » property configuration for each contract deployment.
- Test your signing process thoroughly to ensure that it works correctly.