You did the lvl 30 mission where you rescue Batman from Brainiac in the Batcave and spoke to Batman at the Watchtower after? Still nothing?
I don't know why it's not working. Guess he just doen't have room for another Robin right now. ;)
Yeah, it's not a lvl 30 thing - which you can do before finishing all the missions -it's the last mission you need to do. Then he'll invite you into the special kids room. And give you a sticker.
It was a proud geek moment for me (though mine was with WW, not Batman).
You are not allowed to request a sticky.