How can I override event action for a Universal Analytics tag in a server-side GTM container that receives its hits from a GA4 tag?

Question

This is my situation:

• A client-side GTM container contains a GA4 tag that sends its events to a server-side container containing event_category, event_action, event_label and non_interaction event parameters
• A GA4 client in that server-side container that receives these events
• A Universal Analytics tag (among others) in that server-side container that forwards the events

event_category, event_label and non_interaction are correctly translated to ec, el and ni in the outgoing HTTP request, but somehow event_action isn’t. ea is populated with the value of event instead.

I’ve tried explicitly creating an Event Data variable for event_action and mapping that to event_action in the server-side UA tag, but that didn’t change anything.

So, how can I override event action for a Universal Analytics tag in a server-side GTM container that receives its hits from a GA4 tag?

Answer 1

Found it: It looks like you can override any of the parameters of the outgoing HTTP request by adding x-ga-mp1- plus the parameter to “Override Fields to Set” in the server-side Universal Analytics tag. So in my case that means x-ga-mp1-ea and a couple more:

(Figured this out when trying to add a custom dimension.)