There's got to be a similar market for "push notification as a service". I wouldn't mind giving a company $20 for credits for 500 push notifications. I hit their API, they push to my phone with whatever text I give them.
SMS (twilio) and most chat apps (slack, discord, Facebook messenger, Telegram,GroupMe, etc.) offer this functionality. Is there something you want that using one of these would not satisfy?
I've been using Pushcut on iOS for this purpose, there's a lot of customizability offered including replying with actions. Add in using IFTTT to call the Pushcut notification webhook and then automation gets a lot easier than doing it by hand.