onPostCreated

I have created data collection ‘ExtraPostData’ to add additional data to the blog posts with a reference field called ‘post’ to Blog/Posts collection
I am trying to use the onPostCreated function to add the post to the ‘ExtraPostData’ whenever the post is created following the below code

export function wixBlog_onPostCreated(event) {
    const postId = event.metadata.entityId;
    const memberId = event.entity.memberId;
    const postTitle = event.entity.title;

    return wixData.insert("PostExtraData", { _id: postId, post: postId, _owner: memberId, title: postTitle })
        .catch(err => {
            if (err.errorCode === "WDE0074") {
                return
                Promise.resolve("Post_already_exists");
            }
        })
}

I have tried several events with the post field but it always shows an ‘untitled post’ of the post reference field such as

event.metadata.entityId
event.entity.title
event.entity._id
event.entity.metadata.id

Nothing is working
if there anyone knows what the event I need to use with the ‘post’ reference field