## Account Abstraction Lesson 26: Pay For Transactions zkSync We are very close to having our zkSync account abstraction finished. We still need to pay for the transaction. In the `validateTransaction` function we check to see if we can pay, but now we need to actually do it. We have two possible candidates for this - `payForTransaction` and `prepareForPaymaster`. Since we aren't using a paymaster, we'll be using `payForTransaction`. ```js function payForTransaction(bytes32, /*_txHash*/ bytes32, /*_suggestedSignedHash*/ Transaction memory _transaction) external payable { } ``` Back in the `MemoryTransactionHelper` contract, there is a `payToBootloader` function. This function: - gets the bootloader address - calculates the amount to pay - makes the payment **<span style="color:red">MemoryTransactionHelper.sol</span>** **Pay to Bootloader Function** ```js /// @notice Pays the required fee for the transaction to the bootloader. /// @dev Currently it pays the maximum amount "_transaction.maxFeePerGas * _transaction.gasLimit", /// it will change in the future. function payToTheBootloader(Transaction memory _transaction) internal returns (bool success) { address bootloaderAddr = BOOTLOADER_FORMAL_ADDRESS; uint256 amount = _transaction.maxFeePerGas * _transaction.gasLimit; assembly { success := call(gas(), bootloaderAddr, amount, 0, 0, 0, 0) } } ``` --- Let's use this function inside our function and set it to `bool success`. If not successful, revert. **<span style="color:red">ZkMinimalAccount.sol</span>** ```js function payForTransaction(bytes32, /*_txHash*/ bytes32, /*_suggestedSignedHash*/ Transaction memory _transaction) external payable { bool success = _transaction.payToTheBootloader(); if (!success) { revert ZkMinimalAccount__FailedToPay(); } } ``` Place the new custom errors with the others. ```js error ZkMinimalAccount__FailedToPay(); ``` --- Now we can: 1. Validate the transaction 2. Execute the transaction 3. Pay for the transaction Move on to the next lesson when you are ready.