Getting api key is invalid error

I am trying to access the lightroom API mentioned here - https://developer.adobe.com/firefly-services/docs/lightroom/api/lightroom_edits/

For that I created an OAuth web app client id and client secret and followed the doc for getting the access token - https://developer.adobe.com/developer-console/docs/guides/authentication/UserAuthentication/ims#authorize-request

I am trying to hit the edit API but I am getting 

error. I am using client id in the X-api-key header.
Unable to figure our what's wrong here. I have a lightroom subscription