Hello there, markrougeux.

I'd be happy to add some additional info about the prepayments.

Before doing so, please consult with your accountant to see if they have a preferred method of recording these transactions.

After adding liability account, create a retainer service item by following these steps:

1. Go to Sales > Products and Services.
2. Click New button, and select Service.
3. Enter a name for the new service item (ex. Retainer).
4. From the Income Account drop-down, select the liability account you've created.
5. Hit Save and Close.

Once done, you can create an invoice and use the item for the deposit or retainer payment.

Here's how:

1. Go to + New > Invoice.
2. Select the Customer's name from the drop-down list.
3. In the Product/Service column, select the Retainer or Deposit item you set up.
4. Enter the amount received for the retainer or deposit in the Rate or Amount column.
5. Click Save and close.

When you're ready to charge the customer, you can turn retainers into credit on an invoice and receive it like a payment. Doing this will decrease the amount in your liability account. Then, applies the credit to your customer's invoice, which will turn into income.

Here are the steps:

1. Create an invoice that lists the services or goods you provided for your customer.
2. In the Product/Service field, select the Retainer or Deposit item.
3. Enter the retainer amount as a negative to subtract it from the invoice.
4. Hit Save. 

For more information about prepayments in QuickBooks Online, please read this article: Record a retainer or deposit.

Please feel free to leave a reply below if you have additional questions regarding the prepayment transactions or other concerns. I'm always here to help. Take care and stay safe.