Call this function with parameter argument as array with type 'any'. It will return you json string. Json string is used to submit array in web service call as request input parameter in Swift.

//-----------------------

let array = [["one" : 1], ["two" : 2], ["three" : 3], ["four" : 4]]

let jsonString = convertIntoJSONString(arrayObject: array)
print("jsonString - \(jsonString)")

//-----------------------

func convertIntoJSONString(arrayObject: [Any]) -> String? {

        do {
            let jsonData: Data = try JSONSerialization.data(withJSONObject: arrayObject, options: [])
            if  let jsonString = NSString(data: jsonData, encoding: String.Encoding.utf8.rawValue) {
                return jsonString as String
            }
            
        } catch let error as NSError {
            print("Array convertIntoJSON - \(error.description)")
        }
        return nil
    }