TypeError: "send" and "transfer" are only available for objects of type "address payable", not "address".?

Question

blockchain

pragma solidity >=0.7.0 <0.9.0;

contract Shop {

    function pay (uint amount) public {
        msg.sender.transfer(amount);
    }

    receive() external payable{}
}

wanted to create a simple smart contract that accepts any incoming funds
and sends the amount to the address that requested it

Answer 1

Starting from version 0.8.x, transferring funds (send and transfer) requires the type to be `address payable`, with `msg.sender` becoming just `address` ( documentation link ). Those. you need to cast it to the `address payable` type and the code should work:
payable(msg.sender).transfer(amount);