[concerned_user]

You can, cloudwatch can shut things down on reaching threshold or scale-down.

With cloud you really have to optimize your code/architecture as you pay for what you use.

With your own servers that is not an issue unless you overload them, then you can have an outage.

EDIT: I thought Firebase is amazon for some reason, it is not. So in general Google panel doesn't have that functionality (from my experience with it), they have billing alerts but I never saw anything that would shut off things on reaching that alert.

You can limit by API requests usually but not by credit amount so if you use multitude of API's it can get tricky and they likely didn't limit anything.