Thanks for posting in the Community space, @preserve-machine.
You can record an advance payment by using the Expense feature and use the Accounts Payable as the account to it.
Making an entry for advance payment will record the prepayments as a credit on the supplier's profile, and you can use it to pay their future bills. Let me guide you through the steps:
Once done, when you create a bill in the future, the right-hand sidebar will show you the available credits that you can apply to the bill.
Here's an article you can read for more details: How to record the advance payment made to a supplier.
You can check out these articles that will guide you in recording transactions for your suppliers/customers in QuickBooks:
Keep in touch if you need any more assistance with recording the advance payment, or there's something else I can do for you. I've got your back. Have a good day.