I have come across it in the 23rd episode of the 5th season of Friends. Here is the context:
Joey: This is Vegas man! People will pay to see freaky stuff! Okay, how much would you pay to see this hand (Holds up his left hand) twice? Huh?
Chandler: (Pause) Y'know, I-I can't really put a price on that Joe.
Joey: Hey, are you unsupporting me again?
Chandler: No! No! I support you 100%! I just didn't, I didn't get it right away. Y'know now I'm caught up! Identical hand twins! It's a million-dollar idea!
At first I thought he said I caught on, which after listening again and checking the transcripts he actually didn't. That would make sense to me as catch on means to understand.