How to update comments for any issue type

lekha.a

I am trying to update the comments for Test Execution on cloud version of XRAY and using graphql API's, but not able to get appropriate API to update the comments. 

After lot's of browsing I get following API from REST API V3 as follows:

https://developer.atlassian.com/cloud/jira/platform/rest/v3/api-group-issue-comments/#api-rest-api-3-issue-issueidorkey-comment-post

But this is also not working for me, getting 404 error

{

    "errorMessages": [

        "Issue does not exist or you do not have permission to see it."

    ],

    "errors": {}

}

I am using client ID and client secret to generate the token using below API :

https://xray.cloud.getxray.app/api/v2/authenticate

Please let me know how I can access this API or any other API to update the comments on Test Execution.

Thankyou in advance for any help on this.