How to send push notifications about new Facebook events to an iOS device (Swift)?

Question

Facebook

There is an application. It is necessary to notify the user about new events created on Facebook.
And that at the same time the application was not even launched in the background.
In fact, how Facebook and VK itself work.
How and through which service is it best to implement this?
it is possible without a description of the event, something like "hey you, come here"

Answer 1

Here is the service and instruction https://documentation.onesignal.com/docs/ios-sdk-setup )