I need push notification on mobile webapp (Xojo, iOS+Android), I was thinking to use Twilio Notify Beta but it is not clear to me how it works.
Say a user starts the webapp: first time it should bind with a REST api, but I don't understand where to find the "device token", how to define if the mobile user has to accept the notification or he/she has already did it, etc.
Docs are here.
Can you push me in the right direction?
Twilio developer evangelist here.
You've found yourself among the wrong part of the documentation there I'm afraid.
The section you want is the Notify Usage section which gives you an introduction and then leads on to:
Both articles walk you through how to get a device token, register a binding and send a push notification.
If you are looking to do this for the web too, Twilio Notify supports sending notifications via FCM. You need to require FCM's JavaScript and use that to get a "registration token" which you can also set up as a binding (by following the rest of the Android guide once you have the registration token).
Let me know if that helps at all.