Hi, I am interested in helping you with your firebase notifications, I have worked with Firebase functions for things such as sending an email on registration, notification of a new user sign up. What you are requesting is not too different, but it would be better to see what your database structure looks like on Firebase, and furthermore is this for a mobile application? Do not hesitate to contact me if you have any doubts, concerns or questions, I look forward to hearing back from you soon.