https://stackoverflow.com/q/57698912/1271826

ParseJSON.swift

func parse(message: String) -> String {
    let json = JSON(parseJSON: message)
    return json["Request"]["transactionId"].stringValue
}

let input = """
    {"Request": {"content": {"Reset": {}}, "transactionId": "f7c4d630-552b-46d9-a37d-44450537b48d"}}
    """

let transactionID = parse(message: input)

print("transactionId:", transactionID)

let response = String(format: "{\"Response\":{\"transactionId\":\"%@\",\"content\":{\"Reset\":{}}}}", transactionID)

print("response:", response)

The result of the above, as you’d expect, is:

transactionId: f7c4d630-552b-46d9-a37d-44450537b48d

response: {"Response":{"transactionId":"f7c4d630-552b-46d9-a37d-44450537b48d","content":{"Reset":{}}}}

If it’s failing for you, you might want to add some error checking, e.g.:

func parse(message: String) -> String {
    let json = JSON(parseJSON: message)

    let request = json["Request"]
    if let error = request.error {
        fatalError("request error: \(error)")
    }

    let transactionId = request["transactionId"]
    if let error = transactionId.error {
        fatalError("transactionId error: \(error)")
    }

    return transactionId.stringValue
}