Hello there, Katherine. Let me help you show a vendor discount when paying a bill.

When having a discount on paying a bill, yes, you can enter a discount item into a bill or make vendor credit for the vendor discount. I'll show you how to make a vendor credit:

1. In your QuickBooks, go to +New.
2. Click Vendor credit, and in the Vendor dropdown, choose your vendor.
3. Enter the Category or Item details depending on how you record purchases with this vendor.
4. If done, hit Save and close. 

After that, apply the vendor credit you made to the bill:

1. Select + New and choose Pay Bills.
2. Choose a bill for your vendor from the list. You'll see the available credit with this vendor in the Credit Applied field.
3. Finish the rest of the fields like you usually do.
4. Click Save and close.

On the other hand, I suggest scanning this article to guide you in tracking your bills and recording the payments in QBO: Enter and manage bills and bill payments in QuickBooks Online. 

Comment below for more questions regarding discounts in paying a bill inside QBO. I'll be right back. Take care!