It took multiple calls, but I was finally able to resolve this. In my case, as a former Intuit Online Payroll (IOP) user that was converted to QuickBooks Payroll (QP), the export functionality to QuickBooks Online (QBO) had to be connected by QuickBooks tech support. In short:
1. When I was converted from IOP to QP, the export mapping/link to QBO was also converted and established by QuickBooks. It was working as usual when I began using QP.
2. The export QP to QBO system broke after I had to make some changes to our mapping preferences. Symptoms were identical to yours (the blank window).
3. After multiple calls to QP, I finally found a first tier support person who kept me on the line as she spoke to the "back office" team as they re-established the export connection.
I think this is a known issue. Connecting QP to QBO should be user-implementable. With former IOP users, it appears to require intervention every time you make a change.
