QBO Error: Invalid Reference Id: Invalid Reference Id : Something you're trying to use has been made inactive. Check the fields with accounts, customers, items, vendors or employees.

The error is referring to the accounts, customers, items, vendors or employees that have been archived in QuickBooks Online. To rectify the issue kindly check if it has been deleted/archived if yes, then you have to unarchive then retry the sync in TradeGecko.