Adding the Call parent to the Attendees

I am creating a Call entity with a BPM process. I want the call to be as if the user created it from the activities menu so it needs the attedees to be set.
So I made a task block and inside I added an action (update created entity).

I want to put the newly created call's parent (it's a lead) as an attendee too. I would also like to set the user's status to "accepted".

I tried this:

Code:

array\push(leadsIds, parent.id);

and this:

Code:

leads=parent;

No success so far. How do I correctly do this?