When this occasionally occurs by mistake or human error, every effort is made to withdraw the advertising immediately and no fee is paid to the media owner.
After a few months of trial and error with banner ads and the like, we opted to go with a strict policy that every advertising campaign has a coupon code.
Given how every word for most conference calls is debated and fought for between executive management and attorneys, a simple declaration of error could only be allowed in the presence of demonstrable and continuing success.