Cannot convert value of type '[String : String]' to expected argument type 'HTTPHeaders?'

I´m trying to send mail from my iOS app with Mailgun and Alarmofire I found [this piece of code] 1 but Xcode generates error:

> Cannot convert value of type '[String : String]' to expected argument
> type 'HTTPHeaders?'

Code:

let parameters = [
                   "from": "sender@whatyouwant.com",
                     "to": "anyRecipient@example.com",
                "subject": "Subject of the email",
                   "text": "This is the body of the email."]
    let header = [
            "Authorization": "Basic MY-API-KEY",
            "Content-Type" : "application/x-www-form-urlencoded"]

    let url = "https://api.mailgun.net/v3/MY-DOMAIN/messages"
    Alamofire.request(url,
                   method: .post,
               parameters: parameters,
                 encoding: URLEncoding.default,
                  headers: header)
            .responseJSON { response in
                print("Response: \(response)")
                }

Any suggestions?

You need to set the type explicitly.

let headers : HTTPHeaders = [
    "Authorization": "Basic MY-API-KEY",
    "Content-Type" : "application/x-www-form-urlencoded"
]

To modify existing code create Dictionary exention to cast from [String: String] to HTTPHeaders.

extension Dictionary where Key == String, Value == String {
    func toHeader() -> HTTPHeaders {
        var headers: HTTPHeaders = [:]
        for (key, value) in self  {
            headers.add(name: key, value: value)
        }
        return headers
    }
}

and use this extention to cast it.

AF.request(url, method: requestMethod, parameters: nil, encoding: URLEncoding.default ,headers: header?.toHeader())