Net 45 days after month-end cut-off.

Is this correct?

I think this means you have to pay money for the privious month 45 days after the end of it.

Are there other simple ways to say this?

I don't know what "month-end cut-off" is but "net 30 days" means the entire amount is due 30 days after. So "net 45 days" would mean that the entire amount is due in 45 days. Sometimes, for example, if you pay the amount sooner than that, say within 10 days, you'll get a discount.
Students: Are you brave enough to let our tutors analyse your pronunciation?
Got it! Thanks, GG. Emotion: smile
Hi LiJ

privious should be previous (typo?)
10 points!
Students: We have free audio pronunciation exercises.