What is the way to interact with a user who is offline?

Question

PHP

There are events. There are people who are invited to them and you need to get a response from them about their intention to visit it. I thought to provide an opportunity for the author of the event to send sms. And the recipients would send 1 or 0 in response. The server would process it and everything is ok. BUT!!!!
Users all over the world, and even if sending them sms is not mega expensive, then a reverse sms can cost them a pretty penny.
Does anyone know of a similar way to interact with a user who is offline?

Answer 1

Mobile app with push notifications? In fact, there is no need to groan and gasp, it will not be difficult to make up 3 pages for 3 platforms, and using Cordova it will be even more problematic to make 1 page !