Thanks for writing in, we would love to help you troubleshoot!
In order for a video tag to function properly, the video player needs to be both Vast 2.0 and VPaid 2.0 complaint. The bitmovin player is not one that we are overly familiar with, as many of our publishers utilize JW player for their content. I have attached a video implementation guide that outlines all of the proper requirements, please feel free to take a look.
In order to get a better understanding of your individual account please send your sovrn username directly to firstname.lastname@example.org. We need to make sure that your site is approved and on our master whitelist for the ads to fire properly as well.