Independent Notification service using Ionic, Node & FCM

Hello, I am doing a project on Ionic and I want to use the notification services but I have not been able to make it work.

The idea of ​​the project is that if the user likes a publication, the other user will be notified.

I am using a backend that would perform an independent notification service to the FCM.

If anyone knows of any tutorial or how to do it step by step, I would appreciate it.