Note payment amount doesn't match with what I calculated

[Vince May]

Hi,

I'm new to investing in notes and found a note on FCIexchange and was trying to understand why the payment amount differs from what I calculated the monthly payment should be using the PMT equation. Based on the original balance and the monthly APR, I see that the loan was originally a interest only loan that entered it's fixed rate period. However, when I try to calculate the monthly amount based on the UPB at the start of the fixed period, the monthly amount I calculate with the PMT equation is lower than the payment amount based on the pay history.

I thought I was using the wrong number of periods, however when I built the amortization table, I find the end date to be on target with what was reported. Not sure what I'm missing.