Cannot use Metamask with my smart contract

Question

I am unable to call my smart contract in Metamask over Ganache.

These were the steps I took:

• developed the contract
• tested it successfully using truffle test
• set up a Ganache network and migrated the contract to the network
• in Metamask, connected to the private Ganache network and one of the accounts via private key
• Then proceeded to make a payment from the account of 5 eth and using another account as the "transaction data" in Metamask (see below - the pay contract expects a single address as an argument)

This is the error I'm getting:

This is how I called the contract:

Pay.sol

pragma solidity ^0.4.17;

/// @title Pay - Facilitates payments.
contract Pay {
    event Payment(
        address _from,
        address _to,
        uint amount
    );

    /// @dev Makes a payment.
    /// @param _to Address to pay to.
    function pay(address _to) public payable {
        require(msg.value > 0);
        _to.transfer(msg.value);
        Payment(msg.sender, _to, msg.value);
    }
}

2_pay_migration.js

var Pay = artifacts.require("Pay");

module.exports = function(deployer) {
    deployer.deploy(Pay);
}

Answer 1

That's not how transaction data works. The correct data would be the first four bytes of the keccak256 hash of "pay(address)" followed by the address, left-padded to be 32 bytes wide. As you can imagine, it's unusual to construct that payload by hand. :-)