Certification Aid created a journey and event definition in Marketing Cloud.

To inject contacts into a journey using the REST API, the correct endpoints involve the event definitions and events.

POST /eventDefinitions/key:{key} or /eventDefinitions/{id}: This endpoint allows you to interact with event definitions by key or ID, which is essential for managing journey events.

POST /interaction/v1/events: This endpoint is used to inject events into the journey, thus adding contacts to the journey based on the defined event.