Your campaign may no longer be delivering because it has passed the selected end date for your campaign. For your campaign to continue to deliver more impressions, you will need to create a new Campaign.
An additional reason a campaign might not be delivering is if you have no active creatives. You can view all of your submitted creatives in the campaigns page. Make sure at least one is active for the campaign to deliver.
If you are still having issues, please contact the support team directly. The contact form is available through the Support button in the drop-down menu in the top right corner on the platform.