I have gave it a soothe ball and walked around with it and it has 255 happiness (Unless its not the max) and its not evolving yet. What do I do?
In order to get a Lucario, you must level up a Riolu with high friendship during the day time. If it's not day time, between 10:00 AM and 7:59 PM, your Riolu won't evolve.
I hope I helped!
Make sure its during daytime as that is when it can only evolve