How to allocate landed cost to supplier invoice

Create an expense account named clearing, and then when the additional bills come in:

1. Pay the shipping/customs bill or enter the bill and use that clearing expense account as the expense for the transaction

2. Edit the original bill as follows:
2a. increase the total amount for each item by a portion of the new bill
2b. change to the account portion of the bill at the top, select the clearing expense account, enter the amount of the bill as a negative number
2c. save the edited bill and click though any warning you may get about payments being applied.
2d. Insure the clearing expense account is zero balance, if not go back and adjust the item totals.

QB will use the edited bill to update the purchase cost. If any of the items were sold between the original bill and the additional bills, QB will automatically make the adjustment to the COGS account for the change in purchase cost.

How can I allocate landed cost from 2 different vendors (one for custom duties one for freight) to the same items invoice?

Hi there, @stegag70.

I'd be glad to help you allocate landed costs for different vendors. 

You can use a different expense account. You can go to your Chart of Accounts to create a new expense category. Here's how:

1. Go to the Accounting menu at the left panel.
2. Click on Chart of Accounts.
3. Select New in the upper-right hand corner.
4. Choose Expense or Other Expense for Account Type. 
5. Choose a Detail Type.
6. Enter the name of the new expense category.
7. Type in all other details such as Number or Description.
8. Click the Save and Close button. 

Once done, you can follow the steps given by @Rustler. 

Also, here's an article that can guide you on how to enter and pay bills in QuickBooks Online.

Please let me know if you have additional queries. I'd be glad to help you as soon as I can. Have a great day.