In The Late Late Show, James Corden and Katy Perry talk about starting a business and Katy Perry says "I'm in for a million". What does that mean?
2That she wants to invest one MILLION dollars.– DavoMay 23, 2017 at 19:47
It's a betting idiom: to be in [the game] for some amount.– LambieMay 23, 2017 at 20:03
There is also a related idiom in English: "in for a penny, in for a pound," meaning that a small debt may carry the same consequences as a larger one.– Sven YargsMay 23, 2017 at 20:26
In this context, it means she's interested in investing 1 million dollars in whatever idea they were just discussing.
I'd have to see the clip to give an opinion on whether that's a sincere investment promise or (more likely) a joke as part of a bit.