Declaring parameters. What is the correct way to declare parameters that will be iterated?

I am new to Latex Templates and outputting Rmarkdown This is what my tex file looks like

\documentclass{article}
\usepackage{eso-pic,graphicx}
\usepackage[top=2cm, bottom=2cm, outer=0cm, inner=0cm]{geometry}
\usepackage[absolute,overlay]{textpos}
\usepackage{fontspec}
% Set Font------------------------------------------------
\setmainfont{Segoe UI Symbol}
% Begin Document
\begin{document}
\begin{textblock*}{5cm}(11.6cm,2cm) % {block width} (coords) 
\fontsize{40}{12}\selectfont
 $district_name$  
\end{textblock*}
\begin{textblock*}{5cm}(9cm,3cm) % {block width} (coords) 
\fontsize{24}{12}\selectfont
  $total_membership$ %Param One
\end{textblock*}
\begin{textblock*}{18.6cm}(1cm,8.0cm) % {block width} (coords) 
\fontsize{18}{12}\selectfont
  $lob_one$% Param two
\end{textblock*}
\begin{textblock*}{18.6cm}(1cm,13.0cm) % {block width} (coords) 
\fontsize{18}{12}\selectfont
  $lob_two$% Param three
\end{textblock*}
\begin{textblock*}{18.6cm}(1cm,17.5cm) % {block width} (coords) 
\fontsize{18}{12}\selectfont
  $lob_three$% Param Four 
\end{textblock*}
\begin{textblock*}{18.6cm}(1cm,21cm) % {block width} (coords) 
\fontsize{18}{12}\selectfont
  $lob_four$% Param Five 
\end{textblock*}



\AddToShipoutPictureBG*{\includegraphics[width=\paperwidth,height=\paperheight]{test.png}};
\end{document}

When I write my yaml in Rmarkdown like this, I get the output I want in PDF.

---
title: "Example"
author: "N N"
date: \today

output:
    pdf_document:
        latex_engine: xelatex
        template: test.tex

district_name: "Bob"
lob_one: "Billy B"
lob_two: "Membership 2"
lob_three: "Membership 3"
lob_four: "Membership 4"

---

Fair enough, but in the end goal is to be able to call this rmarkdown and iterate something like this.

renderMyDocument <- function(region, start) {
  rmarkdown::render("MyDocument.Rmd", params = list(
    district_name = something1,
    lob_one = something2
  ))
}

I tried this setup but I did not get the same output as before, in fact none of the params actually appear.

title: "Example"
author: "N N"
date: \today

output:
    pdf_document:
        latex_engine: xelatex
        template: test.tex
params:
  district_name: "Bob"
  lob_one: "Billy B"
  lob_two: "Membership 2"
  lob_three: "Membership 3"
  lob_four: "Membership 4"

What I'm missing here?