As soon as the allotted API calls have been exceeded for the day (100,001 and greater), a 503 error will be returned to the caller for each call after the threshold has been surpassed. This limit is account specific.
If additional calls are required for your environment, please contact your Account Manager.
Related document: API Management APIs
NOTE: If a HTTP Request Rate value is set, API Management uses this limit before the values specified in the API Contract for Rate Limit or Quota Limit.