...a principal sum of $166,667 plus one-time 10% interest charge of $16,667 which matures on May 14, 2018 for $150,000 in cash.
Went back and re-read the terms. The $183,333 was a principal sum of $166,667 plus a 10% interest charge ($16,667). What threw me off was the "for $150,000 in cash." I thought the 10% interest was based off of the $150,000. Which would get you to the $165,000 range.
Strange wording. Generally, the amount issued (i.e. $150,000) is considered the principal amount and everything paid back in addition to the amount owed is interest. It's like there was a 10% loan origination fee on top of the 10% interest. So at the end of the day, Mexus borrowed money at 20% interest.