You can publish a REST or Web service and have that trigger a microflow when called. You can also write your own custom RequestHandlers to trigger actions in your Mendix application.
https://docs.mendix.com/refguide/published-rest-services
https://docs.mendix.com/refguide/published-web-services
https://www.mendix.com/evaluation-guide/enterprise-capabilities/extensibility/
Hope this helps.