429 Throttling Response
The Microsoft Graph API has throttling enabled for APIs. That means after a certain number of calls are made to the API, the Microsoft Graph API server blocks the request for a certain amount of time. In this case, the Microsoft Graph API displays a 429 error.
In this event, the beat is instructed to wait for one minute. The Microsoft Graph API documentation states that this throttling is set to 10,000 requests in 10 minutes.
If the issue still persists, the throttling interval can be manually increased by opening the config file, msgraphbeat.yml, and changing the value of the field throttlingIntervalSecs. By default, it is set to 60 seconds.
For more information, refer to the Microsoft Graph API documentation: https://blogs.msdn.microsoft.com/exchangedev/2017/04/07/throttling-coming-to-outlook-api-and-microsoft-graph/