Unable to add frame numbers to beamer when using Rmarkdown

Question

I write many documents using RStudio, including beamer slides from both LaTeX (Sweave/rnw) and Rmarkdown (rmd).

I understand that \setbeamertemplate{footline}[frame number] will add frame numbers to beamer slides. This works when I use LaTeX, but not when I use Rmarkdown. Specifically, the error is:

l.100 \setbeamertemplate{footline}{[}f
Error: pandoc document conversion failed with error 43

How do I fix this? Or more generally, how do I add frame numbers to a beamer document created with Rmarkdown?

Minimal Example:

Sweave/LaTeX (works):

\documentclass{beamer}
\title{Put Title Here}
\setbeamertemplate{navigation symbols}{} 
\setbeamertemplate{footline}[frame number]{}

\begin{document}
\maketitle

\begin{frame}{Title of Slide}
  Slide text
\end{frame}

\end{document}

Rmarkdown (throws pandoc error):

---
title: "Put Title Here"
output: beamer_presentation
header-includes:
  - \setbeamertemplate{navigation symbols}{} 
  - \setbeamertemplate{footline}[frame number]
---

## Slide Title

Slide text

Thank you.

Answer 1

Summarising information from the answer https://stackoverflow.com/a/38687577/2777074

Create a new .tex file called header_pagenrs.tex which includes the line

\setbeamertemplate{navigation symbols}{} 
\setbeamertemplate{footline}[frame number]

Then in the .Rmd file:

---
title: "Things and Stuff"
author: "Me"
output:
  beamer_presentation:
    includes:
      in_header: header_pagenrs.tex
---