In QuickBooks Online (QBO), if the product has been provided, we can record the down payment and retain the quantity through the deposit box, Evinna. 

To retain the quantity of 17 pieces on the invoice, we need to convert 100% of the Estimate. First, ensure that the Deposit option is enabled from the Gear icon. Next, manually calculate 30% of the total amount of the converted invoice and enter that value in the Deposit box. This will allow us to view the down payment, the remaining balance, and keep track of the item quantity.

Here's how:

1. Open the Invoice converted from the Estimate.
2. Click on the Deposit box below Invoice Total.
3. Manually enter the amount (30%).
4. 
5. Click on the Manage icon and select the Payment options dropdown.
6. Select the Manage Deposit to choose the Payment method and the Deposit account.
   • Note: You can add a memo to add more details related to the transaction (invoice)

However, if the product is not yet provided for this down payment, follow the steps detailed in this article: Record a retainer or deposit. 

As for the Proforma, in QBO, there isn't a separate (Pro-Forma) form template, but you can customize the estimate template to create a Pro-Forma Invoice for your customers.

Check the steps below:

1. Go to Gear, then Custom Form Styles.
2. Click New Style and choose Estimate.
3. Click the Content tab, then the Pencil icon at the top right panel and change "Estimate" from the Form section to "Pro-Forma Invoice".
4. Save the form style by clicking Done.

After you've setup your Pro-Forma Estimate Style, you can create the Estimate by going to + New, then Estimate. Make sure to click the Manage icon at the top of the Invoice and click on the Design dropdown to choose the template you created.

I've also add this article to guide you track your inventory items, such as your best sellers, what's on hand, and the cost of goods in the future: Use reports to see your sales and inventory status.

Feel fee to reply on the thread for any of your concerns. We're always here to help.