EventHubName: Functions 2.x and higher. The name of the event hub. When the event hub name is also present in the connection string, that value overrides this property at runtime.
Connection: The name of an app setting that contains the connection string to the event hub's namespace. Copy this connection string by clicking the Connection Information button for the namespace, not the event hub itself. This connection string must have send permissions to send the message to the event stream.
Reference:
https://docs.microsoft.com/en-us/azure/azure-functions/functions-bindings-event-iot-output