Download starting and just failed what is the wrong point?

I am using this and all my code works fine but when downloading a file via **flutter_inappwebview** it is starting and then failing.

What is the error with this? Here is what my console print.

V/InputMethodManager( 9289): b/117267690: Failed to get fallback IMM with expected displayId=13 actual IMM#displayId=0 view=com.pichillilorenzo.flutter_inappwebview.InAppWebView.InAppWebView{d1b4f78 VFEDHVCL. .F...... 0,0-1080,1458}
I/flutter ( 9289): onDownloadStart https://courseweb.sliit.lk/pluginfile.php/49/mod_forum/attachment/32848/SLIIT%20Covid19%20Reminder%20Students%20-%20Jan%202021.pdf
W/WM-WorkSpec( 9289): Backoff delay duration less than minimum value
D/DownloadWorker( 9289): DownloadWorker{url=https://courseweb.sliit.lk/pluginfile.php/49/mod_forum/attachment/32848/SLIIT%20Covid19%20Reminder%20Students%20-%20Jan%202021.pdf,filename=null,savedDir=/storage/emulated/0/Download/,header=,isResume=false
D/DownloadWorker( 9289): Update notification: {notificationId: 5, title: https://courseweb.sliit.lk/pluginfile.php/49/mod_forum/attachment/32848/SLIIT%20Covid19%20Reminder%20Students%20-%20Jan%202021.pdf, status: 2, progress: 0}
D/DownloadWorker( 9289): Open connection to https://courseweb.sliit.lk/pluginfile.php/49/mod_forum/attachment/32848/SLIIT%20Covid19%20Reminder%20Students%20-%20Jan%202021.pdf
D/DownloadWorker( 9289): Update too frequently!!!!, but it is the final update, we should sleep a second to ensure the update call can be processed
D/DownloadWorker( 9289): Update notification: {notificationId: 5, title: https://courseweb.sliit.lk/pluginfile.php/49/mod_forum/attachment/32848/SLIIT%20Covid19%20Reminder%20Students%20-%20Jan%202021.pdf, status: 4, progress: -1}
D/DownloadWorker( 9289): Server replied HTTP code: 404
I/WM-WorkerWrapper( 9289): Worker result SUCCESS for Work [ id=5af88509-dc48-4e6d-bac2-b88a93989745, tags={ flutter_download_task, vn.hunghd.flutterdownloader.DownloadWorker } ]