How do I parse this nested JSON using Codable with Swift?

First of all: Catch always the DecodingError and print it. It tells you exactly what’s wrong.

The error occurs because you are ignoring the root object Users. Your code works if you decode(Users.self.

My suggestions:

• Decode createdDate as Date adding a appropriate date decoding strategy.
• Decode profileImage as URL (for free).
• Handle all errors.

struct Root : Decodable { // `Users` and `User` is too confusing
    let users: [User]
}

struct User : Decodable {
    let id: Int
    let name: String
    let userName: String
    let profileImage: URL
    let createdDate: Date
}

URLSession.shared.dataTask(with: url) { data, _, error in

    if let error = error { print(error); return }
    do {
        let decoder = JSONDecoder()
        let dateFormatter = DateFormatter()
        dateFormatter.locale = Locale(identifier: "en_US_POSIX")
        dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
        decoder.dateDecodingStrategy = .formatted(dateFormatter)
        let result = try decoder.decode(Root.self, from: data!)
        for user in result.users {
           print(user.userName, user.id, user.createdDate)
        }
    } catch {
        print(error)
    }

}.resume()