I'm trying to implement and use the Solidity claimPayment function so my users(client) can claim a defined amount of tokens on my website (i want them to pay the fees and my server decide how much they can claim).

I ve managed to make everything works (deposits, signing..) but i'm stuck on the claiming function.

First, i generate the signed parameters on my backend server

var bankAddressPrivateKey = '...'; //private key of the wallet that will send the tokens to the client

var USER_WALLET_ADDRESS = '0x....'; //wallet of the client wanting to claim

var decimals = (10 ** 18);
var amountOfTokensToClaim = web3_bsc.utils.toHex(10 * decimals);

var nonce = 1; //just for testing, will be incremented after every claim

var hash = "0x" + abi.soliditySHA3(
   ["address", "uint256", "uint256", "address"],
   [USER_WALLET_ADDRESS, amountOfTokensToClaim, `0x${toHex(nonce)}`, CONTRACT_ADDRESS]

const signedParams = personalSign({
   privateKey: new Buffer.from(bankAddressPrivateKey, 'hex'),
   data: hash,

var data = {
   signedParams : signedParams,
   nonce : nonce,
   amount : amountOfTokensToClaim 

return data;

Then, on the client side, i generate a signed transaction with the signedParams retrieved from the server

var web3_meta = new Web3(window.ethereum);

var contract = new web3_meta.eth.Contract(abiArray, CONTRACT_ADDRESS, {from: USER_WALLET_ADDRESS});

var data = contract.methods.claimPayment(data.amount, data.nonce, data.signedParams).encodeABI();

const transactionParameters = {
   data: data

const txHash = await ethereum.request({
   method: 'eth_sendTransaction',
   params: [transactionParameters],

The Metamask window trigger correctly but i get This transaction is excepted to fail and it fails.

enter image description here

How can i know what's wrong ? There is no detailed error I have double checked that my transaction contain only hex params, and here is the decode input from bscscan testnet:

enter image description here

Here is the my contract code

pragma solidity >=0.7.0 <0.9.0;

contract WLS
    mapping (address => uint) public balances;
    mapping (address => mapping (address=>uint)) public allowance;

    uint private totalSupply = 100000 * (10 ** 18);
    string public name = "Token name";
    string public symbol = "TKN";
    uint public decimals = 18;

    event Transfer(address indexed from, address indexed to, uint value);
    event Approval(address indexed owner, address indexed spender, uint value);

    address owner = msg.sender;
    mapping(uint256 => bool) usedNonces;

    constructor() {

        balances[0x....]= 1000  * (10 ** 18);

    function balanceOf(address user) public view returns (uint)
        return balances[user];


    function transfer(address to, uint value) public returns (bool)
        require(balanceOf(msg.sender)>=value, "Insufficient funds");
        emit Transfer(msg.sender, to, value);
        return true;

    function TransferFrom(address from, address to, uint value) public returns (bool)
        require(balanceOf(from)>=value, "Insufficient funds");
        require(allowance[from][msg.sender]>=value, "Insufficient delegation");
        emit Transfer(from, to, value);
        return true;

    function approve(address spender, uint value) public returns (bool)
        emit Approval(msg.sender, spender, value);
        return true;

    function claimPayment(uint256 amount, uint256 nonce, bytes memory signature) external {
        usedNonces[nonce] = true;

        // this recreates the message that was signed on the client
        bytes32 message = prefixed(keccak256(abi.encodePacked(msg.sender, amount, nonce, this)));

        require(recoverSigner(message, signature) == owner);


    /// destroy the contract and reclaim the leftover funds.
    function shutdown() external {
        require(msg.sender == owner);

    /// signature methods.
    function splitSignature(bytes memory sig)
        returns (uint8 v, bytes32 r, bytes32 s)
        require(sig.length == 65);

        assembly {
            // first 32 bytes, after the length prefix.
            r := mload(add(sig, 32))
            // second 32 bytes.
            s := mload(add(sig, 64))
            // final byte (first byte of the next 32 bytes).
            v := byte(0, mload(add(sig, 96)))

        return (v, r, s);

    function recoverSigner(bytes32 message, bytes memory sig)
        returns (address)
        (uint8 v, bytes32 r, bytes32 s) = splitSignature(sig);

        return ecrecover(message, v, r, s);

    /// builds a prefixed hash to mimic the behavior of eth_sign.
    function prefixed(bytes32 hash) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));

1 Answer 1


ended up using eth.accounts.sign instead of personalSignand it worked.. go figure

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