fall for (a lie)
When someone lies to you or tricks you, and you believe them, you have "fallen for" their lie. So "falling for a scam" means that you were tricked by someone and they took your money.
You use "fall for ___" like this:
A: She said that she had lost her purse and just needed some money to get a taxi ride home.
B: And you fell for that?
I'm not falling for your lies any more!