I've registered on the site and created an app and when clicked on it I was able to see my client ID(5728512) and client tag(C38778329386FEC9B6E2B027A635BDED) but when I sent a request on then I get error in response as json: {"message": [{"value": "Invalid client/user information"}], "response": [{"status": "error"}}} . Can you please help me out of this?

You received this response because you did not provide your Client ID and an User ID in your request.
Assuming you want to register an user, you need to use the register API call, and include your Client ID. Please refer to the Rhythm API quick start guide here:
For other types of requests, you will need to include both Client ID and an User ID.
Hope this helps.