Cognitive Transliterate API

Unable to hit Cognitive transliterate API using subscription ID. Below is the URL & Request body.

https://api.cognitive.microsofttranslator.com/transliterate?api-version=3.0&language=en&fromScript=en&toScript=hi

Header:

1. Content-Type: application/json
2. Content-Length
3. Ocp-Apim-Subscription-Key: Subscription ID(Trying free)

Request Param:

1. api-version: 3.0
2. language: en
3. fromScript: en
4. toScript: hi

Request Body:
[
{"Text":"I am an Engineer."},
{"Text":"Trying the microsoft translator."}
]

Everytime I get 400 error saying: "The request is not authorized because credentials are missing or invalid."

I have subscribed to the Cognitive Translator service on trail basis. I have just received the Subscription ID, what I am using in the "Ocp-Apim-Subscription-Key". is this correct?