Broadcast Tower Mission 4

I was wondering when I get access to the Broadcast Tower mission where I can catch the Delta Solosis? I’m at the 3rd gym right now, and I haven’t gotten notified that the third mission is available yet, so I’m assuming it triggers at a certain point in the story. When might that be?

I remember Suze mentioning that the call for the mission after solosis will trigger randomly after dragon ruins completion. However I don’t remember if there’s any story content past the first thing in 1.2 so not a complete answer and other that than that, I have no idea.