_Follow along with this video:_ --- ### Return to Refund Coming back to the refund function, let's have a closer look. ```js /// @param playerIndex the index of the player to refund. You can find it externally by calling `getActivePlayerIndex` /// @dev This function will allow there to be blank spots in the array function refund(uint256 playerIndex) public { address playerAddress = players[playerIndex]; require(playerAddress == msg.sender, "PuppyRaffle: Only the player can refund"); require(playerAddress != address(0), "PuppyRaffle: Player already refunded, or is not active"); payable(msg.sender).sendValue(entranceFee); players[playerIndex] = address(0); emit RaffleRefunded(playerAddress); } ``` This function takes a player's index, and checks the `players` array for the appropriate address. Following this we see two require statements. ```js require(playerAddress == msg.sender, "PuppyRaffle: Only the player can refund"); require(playerAddress != address(0), "PuppyRaffle: Player already refunded, or is not active"); ``` The first is ensuring that only a player can refund their own ticket/fee. The second, while a little less clear, makes more sense if we see how a player is handled after a refund is processed - their `players` index is set to `address(0)`. So the second require is meant to prevent multiple refunds this way. ```js players[playerIndex] = address(0); ``` Before this however, we see the `sendValue` function being called. This is what returns the `entranceFee` back to the player. --- `sendValue` may look unusual, this is just a simplified method to transfer funds contained within the [**OpenZeppelin Address.sol library**](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/Address.sol). > ```js > function sendValue(address payable recipient, >uint256 amount) internal { > if (address(this).balance < amount) { > revert AddressInsufficientBalance(address(this)); > } > > (bool success, ) = recipient.call{value: amount}(""); > if (!success) { > revert FailedInnerCall(); > } > } > ``` --- ### Wrap Up Already we can see the order of things is going to cause another potential issue. Do you know what it is? Can you spot it?