Sending FCM messages via Cloud functions. Here’s the code:

There is a task to send messages to about 4000 subscribers that the money on the balance has run out. This happens once a month at the same time. I see that you can only send to the topic. Do I understand correctly that I add the right customers to the “top up the balance” topic and then send a message to the group? Are there any restrictions on adding a client to a group if I do it through the API in one fell swoop? _)

I’m trying to implement a notification system using Firebase/FCM and I’m realizing that a naive cron-style implementation to filter users that need to be notified ends up generating a huge # of reads really fast and I’d love to know what’s the canonical way to do this since it seems like a bog standard feature that has been built 100s of times.