Yes, billboard->returned is a string and task->returned is an array. (look at details, there are no quotes)
Construct cant handle Arrays/Objects like this, so it shows 0. (null)
AJAX_RESULTS.Get("id") dont exist. There is only index 0 and 1 in this array. (not a dictionary!)
I dont know the default way to get for example the id value of for example index 0 from returned of AJAX.LastData, in this I cant help you.
I personally would make it like this, with my plugin: