How to append two NSData variable in swift?

Compatible with both Swift 4 and Swift 5 you can only use append function of Data to append two different data.

Sample Usage

guard var data1 = "data1".data(using: .utf8), let data2 = "data2".data(using: .utf8) else {
    return
}

data1.append(data2)
// data1 is now combination of data1 and data2

You need to initialize your messageData before appending to it.

var messageData = NSMutableData() //or var messageData : NSMutableData = NSMutableData()
messageData.appendData(actionIdData)
messageData.appendData(payLoad)