Hi there, directmatters.

Thanks for getting back to us. Allow me to jump in and help ensure to isolate this problem so you keep your QuickBooks up and running. 

I appreciate you for following the steps provided by my colleague on how to turn off the payment service option in QuickBooks preferences. Let's process first troubleshooting steps to resolve the issue about QuickBooks freeze after closing the QuickBooks payments pop-up window. 

Let's use the Refresher Tool, this will ends QuickBooks processes running in the background and also performs mini repair on your QuickBooks Desktop. Here's how:

1. Close all QuickBooks Desktop versions.
2. Download the QuickBooks Refresher Tool.
3. Save the file on your desktop.
4. Run the QBRefresher tool.
5. Re-open QuickBooks Desktop.

If you're still experiencing the same issue, please check this article for the next solutions: Solutions for when QuickBooks stops working.

Once the issue on your QuickBooks resolved, and you still encounter the pop-up window for Merchant login, I recommend contacting the Merchant Service Team to investigate this further.  

You can contact our Merchant team by visiting this link: https://community.intuit.com/browse/payments-contact-us.

Please let me know how it goes. I'll be around to help if you have any other questions about QuickBooks. Have a good one.