It's nice to see you here in the Community, @dodero54.

Let me provide information to help you apply the payment as prepayment in QuickBooks Online (QBO).

To start, you can made an advance payment to a supplier by recording it in QBO using the Expense feature and select the Accounts Payable (A/P) account from the category section. This will set a credit on the supplier section, which you can use for the future bill.

Here's how:

1. Go to the +New and select Expense.
2. Create an expense to the supplier by selecting a Payee and Payment account.
3. Under the Category column, select Account: Accounts Payable (A/P), then enter the description and the amount.
4. Select Save and close.

For reference, you can check this article: How to record the advance payment made to supplier.

Once the bill is ready, you can apply the credit as a payment. Here's how:

1. Go to the Expenses, then select Supplier/Vendors.
2. Click the supplier's name, and find the bill.
3. Under the Action column, click the Pay Bills or Make payment link.
4. From the Bill Payment page, put a checkmark on the check you've recorded under Credits.
5. Hit Save and Close.

I'll also add this article to help you get the most out of your financial reports: Customise reports in QBO.

If you have further concerns about the process of the prepayment, please tag me in the comment section, @dodero54. I'll assist you in any way possible.