Multisig wallet contract written in solidity

multisig.sol

pragma solidity ^0.6.0;

contract Multisig {
    address public owner;
    mapping(address=>bool) public signers;
    uint public numSigners;
    Request[] public pending;
    
    struct Request {
        address to;
        uint amt;
        uint numSigners;
        mapping(address => bool) signers;
    }
    
    constructor() public {
        owner = msg.sender;
        signers[owner] = true;
        ++numSigners;
    }
    
    function addSigner(address addr) external IsSigner() {
        require (!signers[addr], 'signer exists');
        signers[addr] = true;
        ++numSigners;
    }
    function removeSigner(address addr) external IsSigner() {
        require(addr != owner, 'Owner cannot be removed');
        require (signers[addr], 'no signer to remove');
        delete signers[addr];
        --numSigners;
    }
    function sign(address to, uint amt) external IsSigner() {
        (uint requestIndex, bool ok) = findRequest(to, amt);
        if (!ok) {
            requestIndex = pending.length;
            Request memory newReq = Request({
                to: to,
                amt: amt,
                numSigners: 0
            });
            pending.push(newReq);
        }
        
        Request storage request = pending[requestIndex];
        require (!request.signers[msg.sender], 'already signed');
        request.numSigners++;
        request.signers[msg.sender] = true;
    }
    
    function transfer(address payable to, uint amt) external IsSigner {
        (uint requestIndex, bool ok) = findRequest(to, amt);
        require(ok, 'request not found');
        Request memory request = pending[requestIndex];
        require(request.numSigners > 3, "need more signers");
        to.transfer(amt);
    }
    
    function findRequest(address to, uint amt) internal view returns (uint requestIndex, bool) {
        for (uint i=0; i < pending.length; ++i) {
            Request memory req = pending[i];
            if (req.to == to && req.amt == amt) {
                return (i, true);
            }
        }
        return (0, false);
    }
    
    modifier IsSigner() {
        require(signers[msg.sender], 'Only existing signers can add a signer');
        _;
    }
    
    function balance() external view returns (uint) {
        return address(this).balance;
    }
    
    receive() external payable {}
}