How can I make a service in android without notification icon ?

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Android

web

WebSockets

Hi to all,
I am a full stack developer. I'm wondering to find a solution in android background. I'm thinking to write a push notification system for all mobile device types (android,ios) and for web browsers (i mean for web clients). I already have a web-socket server written with nodejs and socketIO. My problem is how can i handle web-socket responses on mobiledevices. At the start point to decide make it with foreground services. But i don't want to show to the users any notification icon on the top. I can not resolve this problem and i don't want to use FCM(Firebase Cloud Messagging) or any third party product i want to make my own background system. I'am ready to learn any programming language for that and if required to work all day and all night.
Thank you very much !

What I have tried:

I am on research phase. I'm thinking to use background services in android version.