Here are the most common reasons for not having a bid:
1. Country: If your ad request is coming from a country with low advertiser interest, then your ad will likely get a "No Bid". The auction is usually strong in countries like US, Canada, Germany, Great Britain, France and other parts of Europe.
2. Very Small Site: If your site gets less than 1000 ad requests per day, then it takes more time for it to get on adveriser's bidding lists. Some of our partners require atleast 20,000 ad requests before they approve a domain and so till then, they might submit "No Bid" responses. As your site gets more popular, it will quickly get on advertiser's whitelists and bidding will improve.
3. Domain Pending: If your domain is showing up as "Pending" in the Domains Report, the ad request may not be sent for auction and will be considered as a "No Bid". Please confirm that all your domains are listed as "Approved"
4. Ad Formats: Certain ad formats have much more advertiser interest than others. For best results, you should use 300x250 or 160x600 ad formats which have the highest advertiser interest. For mobile web pages, 320x50 performs well too.
5. Viewability: If your ad is placed very much below the fold and real users are not seeing it, its possible that your site gets blacklisted and advertisers will submit "No Bid" responses. Most advertisers use sophisticated bidding systems that can change the bid to "No Bid" when they detect that the ads are not being seen by real users.