How does anyone use this software? 12 hours with tech support and they can't process even one payment, track a single estimate, or separate multiple payment installments?

I get that it's important to get this sorted out fast so you can wrap up what you need to do with the progress invoicing and payment. Allow me to join this thread to provide additional information, Liamkays152.

QuickBooks Online and QuickBooks Payments work together by allowing you to seamlessly invoice your customers and receive payments directly through the QuickBooks platform. 
 

Additionally, QuickBooks Payments helps you take care of all your business payments and makes it simple for your customers to pay you. Just be sure to set up your QuickBooks Payments account in QuickBooks Online so customers can pay their invoices online, and then we can process the payments. You can also visit this article to find out when QuickBooks Payments deposits the funds: QuickBooks deposits customer payments into your bank account. 

But if your clients have made the payments and are having issues, I recommend contacting our Payments Support Team again. They'll check your account and see why it's having issues processing payments and its status. Then, they'll tell you how to fix it fast.
 

You can also use the Progressing Invoicing feature. Just turn it on in the settings, and then you can keep track of estimates and make multiple payments from them. For the complete steps, I recommend checking this article: Set up and send progress invoices. If you're having trouble keeping track of estimates, just give me the details. That way, I can look into it and give you the right information. 

In your free time, you can read about converting an estimate into an invoice.

Post again if you require further assistance with your QuickBooks accounts. My goal is to ensure that you achieve your desired outcomes in your bookkeeping.