struct Message:Codable {

let message: String
let timestamp: String
let latitude: String
let longitude: String}

guard let url = URL(string:"http://localhost:443/api/message") else {return}
    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    request.addValue("application/json", forHTTPHeaderField: "Content-Type")
    print("POSTED")

    let newPost = Message(message: "Hi", timestamp: "1", latitude: "1.1", longitude: "2.2")

    print("NewPost:",newPost)

    do {
        let jsonBody = try JSONEncoder().encode(newPost)
        request.httpBody = jsonBody

    } catch let err  {
        print("jsonBody Error: ",err)
    }

    let session = URLSession.shared
    let task = session.dataTask(with: request){ (data,response,err) in
        guard let data = data else {return}
        do{
            let sendPost = try JSONDecoder().decode(Message.self, from: data)
            print("sendPost:(sendPost)")
        }catch let err{
            print("Session Error: ",err)
        }
    }
    task.resume()
}

NewPost: Message(message: "Hi", timestamp: "1", latitude: "1.1", longitude: "2.2")

Session Error:  keyNotFound(DeadDrop.Message.(CodingKeys in _5C64F74710315F52702B56CE54E28C19).message, Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key message ("message").", underlyingError: nil))