Bad notification for startForeground in Androidx

i used NotificationChannel FATAL EXCEPTION: main Process: com.abc.video.downloader:filedownloader, PID: 15527 android.app.RemoteServiceException: Bad notification for startForeground: java.lang.RuntimeException: invalid channel for service notification: Notification(channel=null pri=0 contentView=null vibrate=null sound=null tick defaults=0x0 flags=0x42 color=0x00000000 vis=PRIVATE) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1760) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:201) at android.app.ActivityThread.main(ActivityThread.java:6810) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)