If you are having issue of download file as .bin format on your hybird Android webview app, you may add MIMEtype on DownlaodManger.request as follow:

request.setMimeType(mimeType="audio/mpeg");

Here is a sample code for your ref:

webViewWeb.setDownloadListener(new DownloadListener()
        {
            @Override
             public void onDownloadStart(String url, String userAgent,String contentDisposition, String mimeType,long contentLength) {

                try {
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                        if (ActivityCompat.checkSelfPermission(Objects.requireNonNull(getActivity()), Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
                            // TODO: Consider writing
                            ActivityCompat.requestPermissions(getActivity(),new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, WRITE_REQUEST);

                            return;
                        }
                    }

                    String string = String.valueOf((URLUtil.guessFileName(url, contentDisposition, mimeType)));

                    DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
                    request.setMimeType(mimeType="audio/mpeg");
                    String cookies = CookieManager.getInstance().getCookie(url);

                    String string_d = resources.getString(R.string.downloading_file);

                    request.addRequestHeader("cookie", cookies);
                    request.addRequestHeader("User-Agent", userAgent);
                    request.allowScanningByMediaScanner();
                    request.setDescription(string_d);
                    request.setTitle(URLUtil.guessFileName(url, contentDisposition, mimeType));
                    request.allowScanningByMediaScanner();

                    request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
                    request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS ,  string);

                    DownloadManager dm = (DownloadManager)getActivity().getSystemService(DOWNLOAD_SERVICE);
                    dm.enqueue(request);

                    String string2 = resources.getString(R.string.downloading_file);
                    Toast.makeText(getContext(), string2, Toast.LENGTH_LONG).show();

                    }

        }