The error message you receive indicates that the accounting period in Quickbooks is closed for the expenses that you are trying to export.
Check in Quickbooks if your accounting year is still open for that date:
Edit the closing date if necessary:
After the changes have been made, please synchronise your account under the integrations tab to update the information and try to export again.
Note: It can happen that our OCR made a mistake in extracting the date on the receipt. In this case, check the oldest expense that has been uploaded and which is ready to be exported. If a mistake has been made, you can open it up and correct it.
To find the oldest (completed, approved or controlled) receipt in your expense overview, click on the tab 'date':