I came here to see how to apply firebase fcm notifications. The implementation you mentioned didn't work. Firebase itself changes so quickly that it's so different from the current documentation that it doesn't seem to be helpful to those who are actually applying it. You're talking too much about the main points, so it's hard to follow. Still, you uploaded this lecture for free, and I was able to refer to it because I knew I shouldn't do it this way. Thank you.