Each subscription has a maximum number of requests per minute, called the requests limit. This quota is consumed (decremented) equally with requests to the REST API or by querying graphs in the Studio. Combined graphs may involve multiple simultaneous requests.
The request quota is reset every 60 seconds to the maximum available according to the contracted subscription.
Not all requests involve quota consumption, as explained here.
If the maximum requests per minute are exceeded, the service will provide a response HTTP/1.1. 429 Too Many Requests.