The books are closed for the period in which the invoice is dated. Since the books are closed the invoice will not import into that closed period.
Option 1 (..Unlikely Option) : You can open books in QuickBooks for the previous month again and finish exporting any late invoices for that month and close the books again when completed.
Option 2: Use the Post Month feature in Beanworks. Post month will allow you to post the late invoices from the previous period into the following open period.