How can we create several invoices for one purchase order, in case of partial invoice has been issued by the supplier? Such as 40% invoice first and 60% later.

You've come to the right place for assistance, @s-yoshino. I've got the steps to make sure you can create several bills for a single purchase order in QuickBooks Online (QBO).

Since you'll receive only part of a purchase order, you can add just those parts to a bill or expense. Let me show you how:

1. Click the + New button, then Bill.
2. Select the supplier from the Supplier dropdown. This opens a window with their open purchase orders.
3. Tap Add for the correct purchase order so this adds the items from the purchase order and they'll appear in the Item details section.
4. Adjust the quantity or amount for each line item to reflect the portion you received or plan to pay for.
   
5. Tap Save and close.

Also, the next time you'll create a bill for that supplier you'll see the balance of that purchase order.

For more information about this process: Add purchase orders to expenses, bills, or cheques in QuickBooks Online.

Additionally, you can check out this article that will help you with recording and managing your bills in QBO: Enter bills and record bill payments in QuickBooks Online.

Please know that you're always welcome to post a reply in this thread if you have any other questions about managing your vendors' transactions in QBO. I'll be here ready to assist you. Keep safe!