How do I create a Forum topic post? I'd like to be able to create a topic on an existing forum, using the REST API exposed by the Services module. This is drupal7 and services 3.x .

via the REST interface, I can successfully:


query the index of forums  GET /rest/node?parameters\[type\]=forum
retrieve a single forum post.  GET /rest/node/8
update forum posts (via PUT)  PUT /rest/node/8   ...


I have not been able to create a forum post. 
I tried many different variations of the JSON payload, and have not yet found the secret to success. 

Example:

curl -i -X POST \
  -H Cookie:SESSe6a353351df0bfa8deadcafe=B0ZkiW3-U2x93yJU-deadbeef \
  -H X-CSRF-Token:PSCd5qIdddax0Mh5gfnOM872hdj893-eeeeffff \
  -H Accept:application/json \
  -H content-type:application/json \
  http://myserver/rest/node \
  -d '{
    "title": "This is a test post", 
    "body": {
      "und": [{
        "value" : "This is a test post. Please ignore.",
        "summary": "test1",
        "format": "filtered_html"
      }]
    },
    "type": "forum", 
    "language": "und",
    "status": "1",
    "forum_tid": "8"
  }'


The error looks like this

{
  "form_errors": {
    "taxonomy_forums][und":"An illegal choice has been detected. Please contact the site administrator."
  }
}


I have tried many variations of the payload, and always get the same error. I think the error means I need to pass different data. But I don't know which different data. Help?
Er, yes, I just succeeded in creating a Forum topic, after many trials. This was successful :

curl -i -X POST \
  -H Cookie:SESSe6a353351df0bfa8deadcafe=B0ZkiW3-U2x93yJU-deadbeef \
  -H X-CSRF-Token:PSCd5qIdddax0Mh5gfnOM872hdj893-eeeeffff \
  -H Accept:application/json \
  -H content-type:application/json \
  http://myserver/rest/node \
  -d '{
    "type": "forum", 
    "title": "test post?", 
    "language": "und",
    "taxonomy_forums": {
      "und": "1"
    },
    "body": {
      "und": [{
        "value" : "test post",
        "summary": "this is a test1",
        "format": "full_html"
      }]
    }
  }'


The key difference was, I think, adding this to the JSON: 

    "taxonomy_forums": {
      "und": "1"
    },


I guessed this, based on a view of the Firefox firebug Net panel, when using the UI to post a new forum topic. This number specifies the forum to which the new topic should be associated. It is a different matter to get the list of forum topics!

Maybe this will help others.