Purchase Order generates a popup warning: Account must match the expense account selected category.

Users get this error when:

1) The Expense Category's Account is not an Expense type of Account. To verify this, Navigate to Setup > Accounting > Expense Categories > Edit the Expense Category entered in the Purchase Order.

2)The Expand Account list is not enabled. To enable this, navigate to Setup > Accounting > Setup Accounting or Accounting Preferences > General tab > check the Expand Account List box > Save