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.