You can enable QuickBooks Desktop Web Connector logging by following the following instructions.

Exit the Web Connector

Run regedit (Start > Run > regedit.exe)

Navigating to: \HKEY_CURRENT_USER\Software\Intuit\QBWebConnector

Change the 'Level' key to VERBOSE original is DEBUG

Start the Web Connector, and run your sync

The log file for QBWC can be found at: C:\ProgramData\Intuit\QBWebConnector\log\QWCLog.txt"

This log file will show you both the QBXML request and response send between QuickBooks and the QBWC server.