Getting Error for transfering tokens from wallet address to a smart contract

[Gireeshbd]

this function transfers tokens from wallet to the contract

function InitialSupplyToken(uint256 _SLNSupply)
        external
        onlyAdmin
        preSaleActive
    {
        availableTokens = availableTokens + _SLNSupply;
        SLN.transfer(address(this), _SLNSupply);
    }

But, on the call of this function, this is the error it is showing, the wallet has enough tokens to transfer

{
  "originalError": {
    "code": 3,
    "data": "0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000002645524332303a207472616e7366657220616d6f756e7420657863656564732062616c616e63650000000000000000000000000000000000000000000000000000",
    "message": "execution reverted: ERC20: transfer amount exceeds balance"
  }
}

[alihathim]

did you check your wallet balance?

[mattjaf]

take in account for gas if your trying to empty a wallet

Also make sure your require statements are met

[PatrickAlphaC]

The transfer function looks like this:

function transfer(address _to, uint256 _value) public returns (bool success)

This only transfers tokens from itself. You're looking for transferFrom

function transferFrom(address _from, address _to, uint256 _value) public returns (bool success)

[PatrickAlphaC]

You'll have to call the approve function beforehand. You can check out the erc20 section of the course

https://www.youtube.com/watch?v=gyMwXuJrbJQ&t=49129s