ios google+ api youtube subscribe to a channel - ios

Question

I am trying to subscribe a user to a youtube channel. So the user logs in to an iOS app, hits subscribe, and I would subscribe the user to a predefined channel.
So I have an app created with the YouTube Data API v3 service enabled.
scope: kGTLAuthScopeYouTube
GTLServiceYouTube *service = self.youTubeService;
GTLYouTubeSubscriptionSnippet* snippet = [GTLYouTubeSubscriptionSnippet object];
snippet.channelId = #"UCGRjJrpD2bmk9Ilq6nq80qg";
GTLYouTubeSubscription* subscription = [GTLYouTubeSubscription object];
subscription.snippet = snippet;
GTLQueryYouTube *query = [GTLQueryYouTube queryForSubscriptionsInsertWithObject:subscription part:#"contentDetails,snippet"];
[service executeQuery:query
completionHandler:^(GTLServiceTicket *ticket,
GTLYouTubeSubscription *subscription,
NSError *error) {
/* Callback */
NSLog(#"subscription:%#", subscription);
NSLog(#"error:%#", error);
}];
the server returns:
error:Error Domain=com.google.GTLJSONRPCErrorDomain Code=-32500 "The operation couldn’t be completed. (Required)" UserInfo=0x1005d3c20 {error=Required, NSLocalizedFailureReason=(Required), GTLStructuredError=GTLErrorObject 0x10054faa0: {message:"Required" data:[1] code:-32500}}
Any ideas why would this happen?
I am using the sample youtube app.
The sample url on https://developers.google.com/youtube/v3/docs/subscriptions/insert#examples
works correctly and from what I can tell I am doing the same thing above in objc code.
POST https://www.googleapis.com/youtube/v3/subscriptions?part=contentDetails%2Csnippet&fields=snippet&key={YOUR_API_KEY}
Content-Type: application/json
Authorization: Bearer ya29.AHES6ZQSBniofZhyVX4kfCn0-gVKKeiGayMcQHjTfWxMyffndRus7w
X-JavaScript-User-Agent: Google APIs Explorer
{
"snippet": {
"resourceId": {
"channelId": "UCDPM_n1atn2ijUwHd0NNRQw"
}
}
}
200 OK
Hide headers -
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Content-Encoding: gzip
Content-Length: 286
Content-Type: application/json; charset=UTF-8
Date: Fri, 14 Jun 2013 11:28:26 GMT
Etag: "2vd4g3cVsHAtTjJSdUMaBo1PBVE/Rv5ixqWURoAy7lbp6z3jpkm7IOE"
Expires: Fri, 01 Jan 1990 00:00:00 GMT
Pragma: no-cache
Server: GSE
{
"snippet": {
"publishedAt": "2013-06-14T11:28:26.000Z",
"title": "ColdplayVEVO",
"description": "",
"resourceId": {
"kind": "youtube#channel",
"channelId": "UCDPM_n1atn2ijUwHd0NNRQw"
},
"channelId": "UCQIKfhQEozSerNr3go189mw",
"thumbnails": {
"default": {
"url": "https://i1.ytimg.com/i/DPM_n1atn2ijUwHd0NNRQw/1.jpg?v=c2f0dd"
},
"high": {
"url": "https://i1.ytimg.com/i/DPM_n1atn2ijUwHd0NNRQw/mq1.jpg?v=c2f0dd"
}
}
}
}
UPDATE 1
Enabled loggin - see details below
youtube.subscriptions.insert
2013-06-19 08:45:52 +0000
Request: POST https://www.googleapis.com/rpc?prettyPrint=false
Request headers:
Accept: application/json-rpc
Authorization: Bearer _snip_
Cache-Control: no-cache
Content-Type: application/json-rpc; charset=utf-8
User-Agent: com.boxonline.tpp.bol.think/1.0 google-api-objc-client/2.0 MacOSX/10.8.3 (gzip)
Request body: (214 bytes)
{
"jsonrpc" : "2.0",
"method" : "youtube.subscriptions.insert",
"id" : "gtl_1",
"params" : {
"fields" : "snippet",
"part" : "contentDetails,snippet",
"resource" : {
"snippet" : {
"channelId" : "UCGRjJrpD2bmk9Ilq6nq80qg"
}
}
},
"apiVersion" : "v3"
}
Response: status 200
Response headers:
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Content-Encoding: gzip
Content-Length: 131
Content-Type: application/json; charset=UTF-8
Date: Wed, 19 Jun 2013 08:45:52 GMT
Expires: Fri, 01 Jan 1990 00:00:00 GMT
Pragma: no-cache
Server: GSE
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
Response body: (152 bytes)
{
"error" : {
"message" : "Required",
"data" : [
{
"reason" : "publisherRequired",
"message" : "Required",
"domain" : "youtube.subscription"
}
],
"code" : -32500
},
"id" : "gtl_1"
}

Answer 1

The solution was to replace:
GTLYouTubeSubscriptionSnippet* snippet = [GTLYouTubeSubscriptionSnippet object];
snippet.channelId = #"UCGRjJrpD2bmk9Ilq6nq80qg";
with this:
GTLYouTubeSubscriptionSnippet* snippet = [GTLYouTubeSubscriptionSnippet object];
GTLYouTubeResourceId* resourceObject = [GTLYouTubeResourceId object];
resourceObject.channelId = #"UCGRjJrpD2bmk9Ilq6nq80qg";