SF_10.1, SF_10.2, SF_11.0, SF_11.1, SF_11.2, SF_12.0, SF_12.1, SF_12.2, SF_13.0, SF_13.1, SF_13.2, SF_13.3, SF_14.0, SF_14.1, SF_14.2, SF_14.3 - https://docs.sitefinity.com/for-developers-comment-methods

CommentsRESTApi_CreateComment_JSONFormat.txt

 {
     "Message":"String",
     "Name":"String",
     "Email":"String",
     "CustomData":"String",
     "ThreadKey":"String",
     "Thread":{
         "Key":"String",
         "Type":"String",
         "Title":"String",
         "Language":"String",
         "DataSource":"String",
         "GroupKey":"String",
         "Group":{
             "Key":"String",
             "Name":"String",
             "Description":"String"
         }
     },  
     "Captcha":{
         "Answer":"String",
         "CorrectAnswer":"String",
         "InitializationVector":"String",
         "Key":"String"
     }
 }