Welcome to the QuickBooks family. I'd be glad to assist you with billing expense income and handling advance payments in QuickBooks.
So that I'm able to provide you with the best information, could you please let me know which version of QuickBooks that you're using? The steps are different for each version and knowing the product will allow me to deliver the quickest resolution for you.
I'm looking forward to your reply and further helping you. Wishing you the best.
How do you record the receipt of any income? Do you use customer invoices at all? If not, then the easiest thing to do may be to use journal entries. You could create a journal entry for the date the money was received with a debit to your bank account and a credit to the other current liability account "Unearned Services". Then once the service has been provided, you would create another journal entry on that date to debit Unearned Services and credit your income account.
Welcome to QuickBooks. It really depends on how you received payments and when. If you expect to be paid in the future, send an invoice, if you get paid at the time of sale, record the transaction as a sales receipt.
An easy way to keep track of this is to contextualize the process. Think about how you'd receive documentation of a sale when you go to the store to buy milk - do you get invoiced, or a sales receipt for the milk? And what determined that?
You could accept their advanced payment and record it as a sales receipt to finish the transaction and record it in QuickBooks. However, if you're receiving advanced payments that are refundable (and more like a deposit), there's a separate workflow. Here's how you'd set up a deposit - this method is the best way to stay compliant. Holding money requires a very particular process.
@CGarman has provided some great insight, but I would avoid doing any Journal Entries, it's a bit too powerful for what it sounds like you're trying to accomplish at scale.