ERC20 token transfer to smart contract problem - solidity

Question

I have problem on transfer USDT to Smart Contract .
Please help me.
pragma solidity ^0.6.0;
pragma experimental ABIEncoderV2;
interface IERC20 {
function totalSupply() external view returns (uint256);
function balanceOf(address account) external view returns (uint256);
function allowance(address owner, address spender)
external
view
returns (uint256);
function transfer(address recipient, uint256 amount)
external
returns (bool);
function approve(address spender, uint256 amount) external returns (bool);
function transferFrom(
address sender,
address recipient,
uint256 amount
) external returns (bool);
function increaseApproval(address spender, uint256 amount) external returns(bool);
function decreaseApproval(address spender, uint256 amount) external returns(bool);
event Transfer(address indexed from, address indexed to, uint256 value);
event Approval(
address indexed owner,
address indexed spender,
uint256 value
);
}
contract SimpleBank{
IERC20 tokenContract;
constructor(IERC20 _tokenContract) public {
tokenContract = _tokenContract;
}
function transfer(uint256 amount) external {
address sender = msg.sender;
address reciever = address(this);
uint256 balance = tokenContract.balanceOf(sender);
require(balance >= amount, "balance is low");
bool success1 = tokenContract.approve(sender , amount);
require(success1 , "error on approve");
bool success = tokenContract.transferFrom(sender, reciever, amount);
require(success, "transfer Error");
}
}

Answer 1

The approve() function on the tokenContract needs to be invoked from the token sender directly - not through another contract.
Your snippet effectively approves sender to spend SimpleBank's tokens, as SimpleBank is the msg.sender in the tokenContract.approve() function.