How to add a fallback tag into prebid setup

HeadBidder.net allows setting a fallback tag for tag-based partners (as standard Waterfall). You may use your Google Ad Manager tag and set in GAM account all your tag-based partners and together with the rules there. Thus you benefit twice.

First, you benefit from auction among header bidding partners and GAM (which is also built into HeadBidder.net functionality).

Second, you will continue monetize your inventory through tag based connections.

It might be that you do not have GAM setup, then you can use your own ad server or any other for this purpose, like Revive Ad Server, Aquaplatform, etc.