We were in a similar position and we weren't able to *easily* take a data layer value and send it as a custom event because of how event triggers work in Tealium iQ. Basically, it seems like you can only map events to previously declared "Event triggers" inside GA4's tag mappings as shown here: Essentially you need to map a certain trigger value from your tealium_event UDO data layer key to an event_name. This event_name, however, can't be dynamically set so you can't just take your old UA Event Category and send it that way. At least, I couldn't really find a way to do it. The work around we eventually found was using a tag-scoped Sat Data Value extension that sets tealium_event to a "custom_interaction" value whenever the UDO variables for Event Category, Event Action and Event Label were populated: Then we map an event trigger to tealium_event = "custom_interaction" that sends a "custom_interaction" event: Finally, it's just a matter of mapping the Event Category, Event Action and Event Label variables to event-specific parameters inside the tag: When it's all set up it should look like this: Hopefully this helps. If you really need to map your event_name to the value of Event Category then you could probably do it modifying GA4 tag's template. I personally opted not to because we are trying to deprecate these events anyways and I didn't really want to have to deal with a custom tag this early in GA4s life cycle. Cheers, Joaquín V.
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