This page lists some common issues publishers run into when setting up Prebid.
For example, if your site’s price granularity setup is at $0.10 increment, but the line items are expecting $0.50 increments, bid prices such as $0.71 or $0.99 would not match any line items.
If you have sponsorship line items running, even with lower bid prices, the Prebid line items won’t win. To find out whether you have higher-priority line items running, use your ad servers’ debugging tools, such as the Google Publisher Console.
Check the bid prices. If they are low and are getting reduced to $0 due to price granularity settings, your ad server may choose not to serve them (or you may not have line items targeting $0 bids in your ad server). For example, if you set a $0.50 price granularity and get a bid price of $0.40, the actual price key-value that your ad server will see is $0.00.