REST API Client Issue (Your request did not include an API key) while working with Pentaho Data Integration

I was working with Pentaho Data Integration last week. I faced one issue with REST Client. Actually, I am using REST Client to call MailChimp.

As it describes in below screen shot, I am passing URL from field and method as a post to make a call.

REST client

REST Client Header

I am also passing API key in the header section.  Here api_key_data is stream field and it contains API key in below format. api_key_data = "apikey *************************-us7". 

Yet is giving me error like below

,"title":"API Key Missing","status":401,"detail":"Your request did not include an API key.","instance":""}". 

In fact here I am passing API key. but it is not working with REST API step. 

Solution :

As a solution, I have used HTTP Post step to call the same API with same API key in the header section. 

HTTP Post

HTTP Post Header

and now it is working fine for me.