Cross Domain Tracking with Multiple GA UA Properties, Single GTM Container

I have a client who wants to route page views into separate GA Properties based off a returnUrl UTM. I am trying to configure this in one tag using one GTM container. I know that using cookies for Analytics is changing rapidly and I am having trouble getting everything set up.

Here’s how I have it configured currently:

returnUrl Trigger: enter image description here

That trigger fires a Page View tag configured like so: enter image description here

GTM Preview Fires Everything Correctly, and the Tracking Values are correct: enter image description here

I have added the original domain to Referral Exclusion Lists on each GA Property for the returnUrl domains. But I am not getting page views.

Google Tag Assistant is giving an error of "No HTTP response detected" for the Analytics UA-ID (which is correct).

I’ve seen a lot of different blog posts and tried implementing a few. But I’d like to solve this as quickly and smoothly as possible. I appreciate the help!

Blog posts used:

https://www.simoahava.com/analytics/troubleshooting-cross-domain-tracking-in-google-analytics/

https://www.directom.com/cross-domain-tracking-google-tag-manager/

This post I have looked at but it looks like a lot more Tags / Triggers are involved. Before I bite this off I want to see if there’s a way to save this configuration.

https://www.simoahava.com/analytics/cookieless-tracking-cross-site-iframes/

Thanks for looking!