Flutter: flutter_inappwebview listener (onLoadHttpError) Not Working in Ios

I made a webview app using the flutter_inappwebview plugin that loads a particular site. Now, whenever there's no internet, I want to show a custom error.html file onscreen that is added in the assets folder. All this works perfectly in android but shows a blank screen in ios. There are no errors in the terminal. Relevant code and ios simulator screenshot are below:

                onLoadHttpError: (InAppWebViewController controller, Uri? url,
                    int i, String s) async {
                  /** instead of printing the console message i want to render a static page or display static message **/
                  webViewController?.loadFile(
                      assetFilePath: "assets/error.html");
                } 

IOS Screenshot: https://i.stack.imgur.com/iH9gZ.png

Let me know if additional information is required. This is my first question on SO, please go easy on me.