Sending eth to deployed contract between 2 metamask wallets

Question

 pragma solidity >=0.7.0 <0.9.0;

 contract StructMapping {

    mapping(address => uint) public balanceReceived;

    function getBalance() public view returns(uint) {
        return address(this).balance;
    }  

    function sendMoney() public payable {
        balanceReceived[msg.sender] += msg.value;
    }

    function withdrawAllMoney(address payable _to) public {
        uint balanceToSend = balanceReceived[msg.sender];
        balanceReceived[msg.sender] = 0;
        _to.transfer(balanceToSend);
    }

}

requirements: remix web ide, solidity file with above code opened in remix, two metamask wallets

steps to reproduce:

1. save file and open through remix
2. injected web3 (connect metamask wallet A)
3. deploy contract
4. send from wallet A to the deployed contract using remix interactive feature
5. copy address of the contract and send from metamask wallet B

When I try to perform step 5 the transaction in my metamask from wallet b which is on a different machine fails says not enough gas. How can I send from this remote wallet and have it interact with the contract, im assuming it is just sending it like its a wallet address and timesout.

Answer 1

When you send money to a smart contract, you'll have to call a payable function. It's not possible directly via Metamask, as Metamask merely sends a transaction without any data unless specifically requested to do so via its API. To send send money, you can change your Metamask to wallet B and call sendMoney() function of the contract along with some ETH.

If you want your smart contract to accept money without being called via specific function, you can define a receive function like this.

receive() external payable {
    sendMoney();
}

This tells the contract to accept payment (those sent as normal transactions as you mentioned). This is a security feature of solidity to safeguard accidental sending of ETH to smart contracts which might not have a withdrawal mechanism.