Hello there, @orangzeb.

I appreciate you following this thread and trying the steps provided by my colleagues above. I want to add some information about adding invoice subtotal. I'll make sure you'll be able to add it to an invoice with a partial payment.

As mentioned by one of my colleagues DivinaMercy_N, subtotal will show to an invoice when you click on add subtotal. Another thing is, it will only show for the taxable items. Make sure your invoice has taxable items to have a subtotal after a partial payment.

I'm also adding this article as your reference to customize invoices: Customize invoices, estimates, and sales receipts in QuickBooks Online.

If you have more questions about invoices, leave a comment below. I'm always here to help.