This microflow this actually passed the event (e.g. line) that is currently selected. Add the event entity as input in the microflow. In most cases you will need it.
You need to add a parameter to your microflow:
Drag the highlighted item from the toolbar to your microflow and open to select the object type. Then, where you call this microflow, you need to retrieve the object to pass and put this object in the microflow parameter.:
It would be nice to have a picture of your domain model and see how you did model the reference between a user and an event. Since each user probably can register to multiple events, and that each event has multiple users this is a reference set.
Now the register part. On the page of an event create the subsribe button passing the event object (On click settings, pass entity). In the microflow you now have the event object and you always have the current user. Now it depends if you are working directly with users or may be you created another entity and did you an inherite from user. If you did the last you first need to cast the object before you add it to the reference between event and user.
The error you get is that the microflow did not have an event parameter. Add a parameter to the microflow (the yellow icon when you are in a microflow) and select the event object. Parameters are the method to pass things from forms to microflows. Hope this helps a bit.
See attached: [url=http://postimg.org/image/btnscqqer/][img]http://s13.postimg.org/btnscqqer/microflow.jpg[/img][/url] [url=http://postimg.org/image/9nthi8myb/][img]http://s13.postimg.org/9nthi8myb/model.jpg[/img][/url]