Creating comments for an Idea REST API

I'm trying to create comments using REST API, and according to the documentation, it requires two properties: ContentId and ContentTypeId. When I get the Idea object I can see the ContentId but there is no ContentTypeId, so I can't continue with the process without that. We are using Telligent 10.1.10

Could this be a bug or there is another way to get that property. Thanks