Hi there, @One Auto.
Welcome to the Community. Let me help you enter the transactions in QuickBooks Online.
You'll need to enter two supplier credits in the amount of £18. You'll be applying these transactions to the bill amounting to £412.
To create a credit, here's how:
- Click the + New option in the upper-right corner.
- Select Supplier credit under Suppliers.
- Enter the necessary information.
- Hit Save and close.
- Repeat steps 1 - 4 for the second credit.
Once done, you should be able to see two credits and a bill from the supplier's transaction list. Let's start applying them by making a payment (see screenshot below).

Here's how to apply the credits:
- Open the bill.
- Under Outstanding Transactions, make sure to put a checkmark to the bill.
- Below Credits, put a checkmark on the credits.

- Make sure the amount in the upper-right is zero.

- Hit Save and close.
The bill will now show with a balance of £376 (see additional screenshot).

If you've linked your bank account to QuickBooks, please follow these steps:
- Go to Banking.
- Choose your bank account.
- Search for the expense.

- Select Match.
After the following the steps above, it should zero out the balance of your bill.

You can also check this article for more details about how to handle credits in QuickBooks: Enter supplier credits and refunds in QuickBooks Online.
Please let me know if you need anything else regarding the process. The Community and I will be here to help you.