Freestar does not currently support any implementation of our product with multiple different Google Ad Manager (GAM) accounts being used on a single page. While theoretically possible, if the code is not written to use both GAMs in tandem, attempting to do so can cause a number of unexpected and unintended behaviours as they all share the same command queue through Google Publisher Tags (GPT). Effects you could see would be simple things like ads serving unexpectedly, or not being reported, or more complex issues such as intermittent ad serving failure.
There are multiple elements in GPT that can affect ad serving on a page level. For example, several toggles need to be set before enableServices is called to be active, and functions like "refresh" and "destroySlots" will target all ad slots on page if no arguments are provided. If there are versions of these on page with Freestar that are not wrapped with Freestar's code, this can create race conditions, or cause other unintentional ad behaviour. Please note that this remains true with the Freestar Hosted product as it still uses the GPT library. The Freestar code base is built with the assumption that all GAM functions indicated in the Integration Guide have been wrapped in Freestar's code.
Freestar Ad Server
Freestar Ad Server does not support any publisher's use of GPT on page. Note that any external ad solution that does not use GPT is unaffected.
Publisher Ad Server
If all ad units are in the same GAM, the easiest solution is to wrap all the relevant functions in Freestar's code. As noted above, any external ad solution that does not use GPT is unaffected.
If you are a Freestar publisher and find yourself with one of these conflicts implemented, please reach out to our publisher success team at email@example.com. We can help work through the options available to try to get all elements of your page working together as well as possible.