That means DBP did not receive credit from the advertiser so they can't pay you which is why they were denied. If you go to offers then in the drop down menu on the top right you can view your completed, denied, pending and ignored offers. You can go to denied, select the offer and go to view and it will pop up why you were denied generally it's because the advertiser didn't show you completed it for credit.
Not all of my offers get approved either some do get denied but you can reset all your denied offers by submitting a trouble ticket to try again.