Solved: dyld: Symbol not found: _OBJC_CLASS_$_NSURLSessionWebSocketMessage

This error was occurred when run the app on an iOS device with OS version less than 13, after investigate the problem was caused by the ktor library, I find when I added ktor library to the application, the app will crash with the above error. And I try to downgrade the ktor, the latest version is 2.0.3 , and when I downgrade to 1.6.8 the application can run.

Another problem is send message to websocket with the following code:actual fun sendMessage(msg: String) {
   val message = NSURLSessionWebSocketMessage(msg)
   webSocket?.sendMessage(message) { err ->
       err?.let { println("send $msg error: $it") }
   }
}

In the method, it uses a class named NSURLSessionWebSocketMessage , but from apple’s document, this class is available for iOS 13+ , so if there are code reference NSURLSessionWebSocketMessage , it will report this error.