Problem with implementing ERC-20 interface in Solidity contract

Question

I'm trying to implement contract which interacts with ERC-20 via interface. Code of interface was taken from openzeppelin github.

The problem is that it fails any transaction which triggers contract func.

What have I done wrong? :(

Example: Following func checks if sender has enough tokens of ERC-20 and sender allowed to spend tokens earlier. If conditions are success it transfers tokens from sender to custom contract address.

    function deposit(uint256 amount) public {
        require(tokenContract.balanceOf(msg.sender) >= amount, "Sender has not enough balance");
        require(tokenContract.allowance(msg.sender, address(this)) >= amount, "Contract is not allowed to transfer tokens");
        require(tokenContract.transferFrom(msg.sender, address(this), amount) == true, "Could not send tokens from the buyer");
    }

Extra info:

• sender has enough tokens to spend
• sender has approved custom contract before transaction

Failed transaction url: https://rinkeby.etherscan.io/tx/0x8df7513a0da10645ce3e300399e73bb58d28dcb8bddb92bddf40945751ae69fc

Sample contract code url: https://rinkeby.etherscan.io/address/0x479a28cff2194a67ccb95ddb960d09fcbb127462#code

ERC-20 (USDT) contract code url: https://rinkeby.etherscan.io/address/0x75cb130d6bbd3d915b34573dc3dd3fb45184f12f#code

Answer 1

That contract doesn't follow the final ERC20 specification.

The declaration for transferFrom doesn't return anything:

function transferFrom(address _from, address _to, uint _value) public;

The calling contract defines transferFrom returning a bool instead:

function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

OpenZeppelin provides the SafeERC20 library that is a wrapper that allows interacting with this type of contracts.