CommentThreads.list() with channelid or allThreadsRelatedToChannelId as parameter gives HTTP 403 error

I am trying to get all the video comments of a specific channel https://www.youtube.com/channel/UCRTxkfOMHehmuD2kGcAS2bg. And I am getting the below error.

{"error": {"code": 403,"message": "The video identified by the \u003ccode\u003e\u003ca href="/youtube/v3/docs/commentThreads/list#videoId"\u003evideoId\u003c/a\u003e\u003c/code\u003e parameter has disabled comments.","errors": [{"message": "The video identified by the \u003ccode\u003e\u003ca href="/youtube/v3/docs/commentThreads/list#videoId"\u003evideoId\u003c/a\u003e\u003c/code\u003e parameter has disabled comments.","domain": "youtube.commentThread","reason": "commentsDisabled","location": "videoId","locationType": "parameter"}]}}

Note:- I have tried getting the video comments for the other channels and there is no issue with the response as above.

Please throw some light on this and provide the official api docs if possible.