Thanks @Shubham.
I have read carefully the post “Add headers using virtual service” you referred before creating this post. The answer is confusing. as it is out of context of a VirtualService. I tried to use that answer in my config above. And this seems NOT to work (in Firefox Dev Tool, I don’t see the custom header added to the http request)
In that post, at the end, member “roquesao” asked practically the same question as this post. There was no answer.
This seems trivial but I am confused by itsio doc (no example and no mention of array in the headers filed) and the yaml syntax. If you know the answer, can you please fix the YAML I mentioned in the original post?