You need a database of everyone who signs up for the service so you can know who to send notifications to. That database needs some kind of unique ID plus a regular location updates.
That's a tempting target to go after, as it's a list of potential ICE targets plus 'political sympathizers'. The app developer does not (AIUI) want the responsibility of keeping that database secure against attack, exposure, or warrant requests.
I wonder if there are tor proxies that accept incoming https, and forward to service endpoints that opt in.
That’d help.
Anyway, the first step is getting it working at all.