Why is push sent to FireBase, but it does not come to devices?

Question

Kotlin

Good day! Spent all day wondering why push notifications are not coming to my Android devices.

I still can’t understand, but I’ll explain the essence: there is a mobile application that is written in Kotlin, it is connected to FireBase and works properly, all the statistics are displayed and work correctly, but when I send notifications to my devices they don’t come, what happens that they went successfully to the devices, but there are no notifications on the devices. Maybe I missed something?