Hi Rose! Welcome to Meta.
The Discourse Hub app on iOS only supports push notifications for Discourse sites hosted by the Discourse team. From the app description on the App Store:
- Real time push notifications for officially hosted Discourse forums
This is due to the way push notifications work on iOS devices - we need a certificate from Apple, which must remain private, and thus can only be used by sites we host. You’ll still receive notifications, but only when the schedule on iOS runs, not live. For live iOS push notifications on non-hosted sites, check out Pushover notifcations.