I'm researching Firebase Cloud Messaging in order to use it as a messenger on a platform where there will be web systems (Java, Spring) at one end and the other App's (ionic) - both with a RestFull (Spring Boot) API.
However, I did not find demo content to make the web system (backend) sign up as a messenger client . Is it possible to use FCM in this model? If so, please share some content or tip.