I labeled your post with the request attributes label - I hope that way the experts on that topic will spot your question quicker 🙂
Have a great day and enjoy the Dynatrace Community!
Ah sorry I now I get it.
If you look at the Request Attributes for the top service in that PurePath, it will only pick attributes from that node for the data sources.
The header in the screenshot is not on the request to the initial service but on a downstream call to an external service (Request to public network). That's why it is not picking it up.