First of all, make sure you haven’t requested to close your campaign, as this means the campaign has been definitively closed.
If not, you can reactivate your campaign and keep collecting funds. Go to the “Edit” section of your campaign and change the date in the field “End date of your campaign”. Be aware that you need to choose at least the date of tomorrow. Make sure the status of your campaign is “published” and save your changes.
Your campaign is now ready to collect funds again.