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I have tried 2 days working on transerFrom. But notworking so please help me.

I know we need to approve() first. Approve() and Allowance() seem to be fine. I read this FAQ( https://forum.openzeppelin.com/t/transferfrom-always-reverts-with-revert-erc20-transfer-amount-exceeds-allowance/3993 ) but ... not working. I read this one too. ERC20 - Approve & TransferFrom not working

Here is what I did.

What I want to do is for example,

  1. Tom send 10 BUSD to my contract X.
  2. Contract X send TOKEN A to Tom.

In Solidity(based on remix)

  1. Tom approve 10 BUSD ⇨ contractX.approve(Tom's Address, 10)
  2. Tom send function buyToken ⇨ contractX.buyTokens(10)

Here is my code code

function approveBUSD(address _spender, uint256 _value) public returns (bool) {
   return tokenB.approve(_spender, _value);
}

function buyTokens(uint256 amount) public payable {

uint256 allowance = tokenB.allowance(address(this), msg.sender);
require(allowance >= amount, "Check the token allowance");


tokenB.transferFrom(msg.sender, address(this),amount);

emit BoughtTokens(msg.sender, amount); // log event onto the blockchain

I created two Solidity Contract. One is for TOKEN A issue. The other is this exchange program.

Token A transfer seems to be okay. But my contract can't accept BUSD. Even the BUSD approve seems fine..

Error message is

Internal JSON-RPC error. { "code": 3, "message": "execution reverted: insufficient allowance", "data":

So buyTokens(0) completely works!....

Please help me. I will give you tips...

Thank you in advance.

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I have finally successed.

I stopeed to use remix. I just used from web3.

haha,,,

IERC20.approve(spender, amount) thinks the owner is also the contract

thanks to this post

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