I've got you covered, @1231 4600 7539 879.

You'll have to make sure that the expense or check transactions link to Accounts Payable (A/P). Let me discuss this with you in detail and help you from there.

The Credits section will only show on the Bill Payment page if you have selected Accounts Payable (A/P) to any expense or check transactions. To make sure, let's open your expense or check transactions and select Accounts Payable as an affected account. Here's how:

1. From the left menu, click Expenses.
2. Select the appropriate expense or check transactions.
3. In the Category details section, select Accounts Payable (A/P) under the Category column.
4. Click Save and close.

I've got you an article for more details: Enter a Credit from a Vendor.

Once done, you'll be able to see the Credits section on the Bill Payment page. I've got screenshots below for your visual reference.

In case you need tips and related articles in the future, feel free to visit our QuickBooks Community help website for reference: QBO Self-help. 

Don't hesitate to leave a comment below if you have any other questions. I'll be right here to help.