problem with blogger java v3 api authentication

Hi
I'm trying run a sample post insert using Blogger JAVA v3 api and running 
into issues.   Please let me know what I'm missing or doing incorrectly or 
my setup is incorrect.
Our applications runs periodically without any user interaction and 
automatically post to our blog.  Process runs on a stand alone machine 
without any user interaction. It was working fine before gdata was 
deprecated.   

I took the following steps:
1. enabled Blogger API v3 in developer console.   
2. created a service account under credentials and downloaded .p12 file.   
(I assume service accounts are supported since 
google-api-services-blogger-v3-rev48-java-1.20.0 has calls 
like setServiceAccountId, setServiceAccountScopes 
and setServiceAccountPrivateKeyFromP12File).
3. downloaded google-api-services-blogger-v3-rev48-java-1.20.0

Running code below and getting, this error:
com.google.api.client.googleapis.json.GoogleJsonResponseException: 403 
Forbidden
{
  "code" : 403,
  "errors" : [ {
    "domain" : "global",
    "message" : "We're sorry, but you don't have permission to access this 
resource.",
    "reason" : "forbidden"
  } ],
  "message" : "We're sorry, but you don't have permission to access this 
resource."
}
at 
com.google.api.client.googleapis.json.GoogleJsonResponseException.from(GoogleJsonResponseException.java:145)
at 
com.google.api.client.googleapis.services.json.AbstractGoogleJsonClientRequest.newExceptionOnError(AbstractGoogleJsonClientRequest.java:113)
at 
com.google.api.client.googleapis.services.json.AbstractGoogleJsonClientRequest.newExceptionOnError(AbstractGoogleJsonClientRequest.java:40)
at 
com.google.api.client.googleapis.services.AbstractGoogleClientRequest$1.interceptResponse(AbstractGoogleClientRequest.java:321)
at com.google.api.client.http.HttpRequest.execute(HttpRequest.java:1056)
at 
com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:419)
at 
com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:352)
at 
com.google.api.client.googleapis.services.AbstractGoogleClientRequest.execute(AbstractGoogleClientRequest.java:469)
at testAuth.main(testAuth.java:136)

-------------------------------------------
my code:
try {
HttpTransport httpTransport = GoogleNetHttpTransport.newTrustedTransport();
JsonFactory jsonFactory = JacksonFactory.getDefaultInstance();

 GoogleCredential credential = 
new GoogleCredential.Builder()

.setTransport(httpTransport)

.setJsonFactory(jsonFactory)

.setServiceAccountId("[email protected]")

.setServiceAccountScopes(Collections.singleton(BloggerScopes.BLOGGER))

.setServiceAccountPrivateKeyFromP12File(new File("xxxxxxxxxxx.p12")) 

.build();


Blogger blogger = new Blogger.Builder(httpTransport, jsonFactory, 
credential)
.setApplicationName("My Project")
.build();

// Construct a post to insert
Post content = new Post();
content.setTitle("A test post");
content.setContent("With <code>HTML</code> content");

String TEST_BLOG_ID = "xxxxxxxxxxx9897";

Insert postsInsertAction = blogger.posts().insert(TEST_BLOG_ID, content);

// Restrict the result content to just the data we need.
postsInsertAction.setFields("author/displayName,content,published,title,url");

// This step sends the request to the server.
Post post = postsInsertAction.execute();   //fails here

// Now we can navigate the response.
System.out.println("Title: " + post.getTitle());
System.out.println("Author: " + post.getAuthor().getDisplayName());
System.out.println("Published: " + post.getPublished());
System.out.println("URL: " + post.getUrl());
System.out.println("Content: " + post.getContent());

} catch (GeneralSecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

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