This event type is only dispatched when your app is rate limited on the Events API. Rate limiting currently occurs when your app would receive more than 30,000 events in an hour from a single workspace.
Here's a field guide:
token - the same shared token used to verify other events in the Events API
type - this specific event type, app_rate_limited
minute_rate_limited - a rounded epoch time value indicating the minute your application became rate limited for this workspace. 1518467820 is at 2018-02-12 20:37:00 UTC.
team_id - subscriptions between your app and the workspace with this ID are being rate limited
api_app_id - your application's ID, especially useful if you have multiple applications working with the Events API
This event does not require a specific OAuth scope or subscription. You'll automatically receive it when your app's event subscriptions are rate limited or disabled.
Event subscriptions may be limited and disabled when your app does not respond with a HTTP 200 OK to at 5% of event deliveries in the past 60 minutes.