When the ad network experiences time-outs due to the lengthy creative load time or does not have an eligible ad to show (no fill), it should properly call MoPub’s failover tag. Proper implementation of the failover tag will ensure that our ad server can call the next item in the waterfall based on priority.
If the network is not able to implement it on their end, make sure to move the network at the end of your waterfall to avoid issues with fill rate and revenue loss for the ad unit.
The passback/failover tag below is a MoPub SDK only feature and can only be used by Custom Networks (JS tags).
MoPub failover tag should be called synchronously, before any other content. If not implemented properly, there have been known impression discrepancies and problems with the delivery of budgeted line items.
Synchronously: scripts are loaded sequentially, one after another, starting with the tag
Asynchronously: some scripts can be loaded simultaneously; this implementation can result in MoPub to recognize the load as if it’s a full ad response and fire an impression pixel when there is no ad shown to the user.
MoPub Failover tag:
Please review the articles below for more information: