Swift Recap Part 2

Hello, I have been working through this code challenge and I'm wondering what part of my code is incorrect? I run it in Xcode and it works just fine, however when I try to submit it, I keep getting an error.

Here's the question:

For this task, add an instance method to Post.

Name the method description. It takes no parameters and returns a string that describes the post instance. For example given a title: "iOS Development", author: "Apple", and a tag named "swift", the description would read as follows"

"iOSDevelopment by Apple. Filed under swift"

Once you have an instance method, call it on the firstPost instance and assign the result to a constant named postDescription

Any help would be greatly appreciated! Thank you!

struct Tag {
    let name: String
}

struct Post {
    let title: String
    let author: String
    let tag: Tag

    init(title: String, author: String, name: String) {
        self.title = title
        self.author = author
        self.tag = Tag(name: name)
    }

    func description() -> String {
        return "\(title) by \(author). Filed under \(tag)."
    }
}

let firstPost = Post(title: "Code challenge", author: "Hussein Kheireddine", name: "Hussein")

let postDescription = firstPost.description()