The math doesn’t seem to add up. You said the investors would earn on average 6% return on their investment meaning that your client is receiving more than 6% to be able to pay that back to investors. If we’re conservative and say 12 people all invested 70k, that leaves 50.4k in profits. Based on that not sure we’re the 500k in revenue was generated?

If your client earned 500k from those 12 investors, then you’re talking about a 60% ROI. If that’s the case then I’d credit your clients secret success on whatever this magic investment is, not your email.