Missing { inserted in R markdown

[Guy Abel]

Keep getting a message:

! Missing { inserted. <to be read again> \left l.70 \end{frame}




when running the R markdown file below. I have spent a few hours pulling my hair out trying to figure out why? The equation renders in the preview fine.

---
title: "Untitled"
output: beamer_presentation
---

## R Markdown

$$ f(x) = \left( 1 + \frac{x}{m - \alpha} \right) ^ \left( x \right) $$