How do I create a supplier opening balance that is in credit? i.e. they owed me money at the date of opening

I'm glad to assist you in entering a supplier opening balance in QuickBooks Online (QBO), @Michael385.

When linking a bank account or credit card to QBO, opening balances are crucial. They aid in ensuring that QBO precisely matches your bank records from the date you started.

If a supplier is newly created and has no associated transactions, enter the opening balance as a negative.

Here's how:

1. Go to Expenses and select Suppliers.
2. Click New Supplier.
    
3. Enter the necessary details and go to the Additional Info section. Enter the amount as a negative in the Opening balance section.
4. Click Save.
   

    

Otherwise, create a supplier credit to record what they owe in QBO. 

Furthermore, you can run dozens of reports that inform you about the different aspects of your business.

Let me know whenever you have further questions. The Community is always available to assist you. Take care and have a good one!