With the limited information above, I dont think you need to pay it. First and last is all that's required, they can't raise rent for a year, and you never need to sign another lease with them, you go 'month to month' after.
They're allowed to ask you for $50, just like I can ask you for $50. Doesn't mean shit and you can say no.
That being said, be nice but be firm. Ask what it's for and then do specific research to see if its allowed. If it is, ask for time to pay it, if not, say no.
Oh yeah?!? Well, brexit!