You can run the Transaction Detail by Account report and then customize it to all vendors, bills, and expenses to see if the transactions are assigned to a Project.
Here's how:
Go to the Reports menu.
In the search field, type in Transaction Detail by Account.
Click the Customize button in the upper right hand.
Set the Report period and Accounting method.
In the Rows/Columns section, select Date, Transaction Type, Number, Name, Amount,and Vendor.
In the Filter section, select Bills and Expenses for Transaction Type.
Choose the account that you want to show in the Account drop-down.
Hit Run report.
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