How can i add a comment using GRAPH API in Planner

Hello,

Sorry "A year later", I was looking to do the same thing and find this post.
I used https://developer.microsoft.com/en-us/graph/docs/api-reference/beta/api/conversationthread_reply to understand how to publish a new comment from Graph

with POST https://graph.microsoft.com/v1.0/groups/[GroupID]/threads/[ConversationID]/reply

And body content like

{
  "post": {
    "body": {
      "contentType": "1",
      "content": "Hello from Graph"
    }
  }
}

To find the conversationID i use:
https://graph.microsoft.com/v1.0/groups/[GroupID]/threads

or

https://graph.microsoft.com/v1.0/Planner/Plans/[PlanId]/tasks
or
https://graph.microsoft.com/v1.0/Planner/tasks/[TaskID]

To find PlanID or GroupId, just browse to you planner, it's in the URL

Let's play with this :)

/Christophe