3_5_business_days

My friend gave me this cipher for the crypto in this new cool app we're building together, but I suspect there are some flaws in it. He told me he'd get back to me in 3-5 business days but it's been 3 weeks....

Can you figure out what's wrong?

Edit: A small change was made to the problem, make sure you're using the most up to date version of the chal.py.