Please specify which API your are trying to use.
if you’re talking about Mendix Platform API, I think Mendix don’t have rate limiting as of now.
if you’re talking about Your own API application then it’s up to you how you implement rate limmiting for you API system.
atm there are no limits on the calls you can make to the MxPlatform API’s
Also all outgoing/incomming API from/to your Mendix app aren’t restricted by Mendix.
Only ristriction you might have are the restrictions of 3rd party API’s you are consuming