Thanks for sharing your detailed concern in the Community, @alchuikov. I’m here to help and impart some information about handling advance payments in QuickBooks.

The sales form you used for advance payments is correct. However, QuickBooks Online offers a specific way to handle prepayments, so your reports are accurate and balanced.

You can set up a deposit or retainer. This option is treated as a liability to show that the amount you’re holding won’t belong to you until it's used to pay for services.

Before you create a retainer item, you need to make a liability account first to track the amount of the retainers you receive from your customers.

Here’s how:

1. Go to the Gear icon, then select Chart of accounts.
2. Press New.
3. From the Account Type drop-down, select Other Current Liabilities.
4. Choose Trust Accounts - Liabilities from the Detail Type drop-down menu.
5. You can enter “Trust Liability” in the Name field.
6. In the question, When do you want to start tracking your finances from the is an account in QuickBooks? Choose an option.
7. Click Save and close.
   

Once done, you can now create an item in the program. I’m glad to show you the steps.

1. Select the Gear icon, then go to Products and Services.
2. Click New.
3. From the Product/Service information panel, select Service.
4. Enter a name (ex. Retainer).
5. From the Income account drop-down menu, select Trust Liability account.
6. Select Save and close.

For the rest of the steps, check out this article: Record a retainer or deposit. Just proceed to Step 3-6.

You can also read this reference for more information on how to handle advance payments: Accepting advance payments.

I’ve added this link that contains topics about managing payments: Process customer payments with QuickBooks. I'm sure you'll find it helpful.

Don’t hold back to drop a comment below if you have any other questions or concerns about sales forms and reports. I’ll be here. Have a good day and always take care!