User tries to sync vendor bills from BillQuick Online to QuickBooks Online but gets the following message:
Vendor bills sent to QuickBooks but errors were encountered. Please see the log file.
If you go to the sync log, it shows this:
The reason for the errors is that QuickBooks Online Essentials does not include inventory and item tracking. 
You might want to upgrade to the higher edition/flavor of QuickBooks Online to include this feature. See this comparison chart for more: https://quickbooks.intuit.com/t/qbks-13588/c/pricing/