When making a lot of API calls to the SESC (Symantec Endpoint Security Complete) tenant, calls may begin to fail if making a lot of calls (such as 2000+ a minute that was happening in once case). Errors will depend on how the application making the calls display them, such as "Error, service too busy", or "Connection refused".
SESC with 3rd party application making API calls to the SESC API services
A 5000 calls per hour limit has been set to avoid causing performance issues for all Tenants in the region.
This is working as designed. Please adjust the number of API calls being made at any given time.