Thanks @Marc-Andre_Lafleur ! In my current use case I'm using Python. I did expect that a PoSH example would be easier. Will try the structure you use above.

My code to construct the comment:

\n        # Create comment object\n        base_id = str(uuid.uuid4())\n        display_name = str(uuid.uuid4())\n        current_datetime = (str(datetime.datetime.now().isoformat()))\n        comment = {\n            \"BaseId\" : base_id,\n            \"ClassName\" : \"System.WorkItem.TroubleTicket.AnalystCommentLog\",\n            \"ClassTypeId\" : \"f14b70f4-878c-c0e1-b5c1-06ca22d05d40\",\n            \"Comment\" :  comment,\n            \"DisplayName\" : display_name,\n            \"EnteredBy\" : str(user.get('DisplayName','API-User')),\n            \"EnteredDate\" : current_datetime,\n            \"FullClassName\" : \"Trouble Ticket Analyst Comments\",\n            \"FullName\" : f\"System.WorkItem.TroubleTicket.AnalystCommentLog:{display_name}\",\n            \"Id\" : display_name,\n            \"IsPrivate\" : isPrivate,\n            \"LastModified\" : current_datetime,\n            \"LastModifiedBy\" : str(user.get(\"BaseId\",\"7431e155-3d9e-4724-895e-c03ba951a352\")),\n            \"Path\" : None,\n            \"TimeAdded\" : current_datetime,\n            \"Title\" : \"Analyst Comment\"\n        }\n        # Deep copy original work item formJSON\n        #logging.info(wi.json)\n        original = copy.deepcopy(wi.json)\n        # Reference original work item\n        current = copy.deepcopy(wi.json)\n        \n        # Append comment object to array\n        current.get('AppliesToTroubleTicket').append(comment)\n        \n        formJson = {\n            \"formJson\" : {\n                \"original\" : original,\n                \"current\" : current\n            }\n        }\n        # Update Current Projection LastModified\n        formJson['formJson']['current']['LastModified'] = current_datetime\n        \n        logging.info(f\"AddComment :: {json.dumps(formJson)}\")\n        try:\n            response = Projection.CommitProjection(formJson=formJson, concurrency_check=True)\n            return response\n        except:\n            logging.error(\"Unable to submit System.WorkItem.TroubleTicket.AnalystCommentLog\")\n            return False

Is it possible to create System.WorkItem.TroubleTicket. AnalystCommentLog via the Cireson API?