So, I am on a project, where the user can select an option and the output pdf should be generated accordingly as a pdf report. The Shiny app does work well and the pdf report too. I would like to just go one step further and customize the pdf report’s styling to make it visually more attractive. To that end, I am pretty much using a similar customized pdf styling that I found online. However, I am having difficulty to apply the customized pdf style, written in .tex, to the dynamic pdf report made with RMarkdown. So, here is a sample code from the R Markdown document;

---
title: "`r unique(data_selected$aaa)` - AAA"
subtitle: BBB
geometry: margin=1in
output:
  pdf_document:
    latex_engine: xelatex
    fig_caption: true
    keep_tex: true
    includes:
      in_header: pdf_report_styling.tex
---

# Header 1

some text here

`{r aaa}

data <- read_excel("data.xlsx")

data_selected <- data %>%
  filter(aaa == data$aaa)

table_gt <- data_selected %>%
  gt() %>%
  tab_style(style = list(cell_fill(color = "lightgray")),
            locations = cells_body(columns = everything())
            )
table_gt

And the .tex file I am using to customize my pdf report is this;

% load packages
usepackage{geometry}
usepackage{xcolor}
usepackage{eso-pic}
usepackage{fancyhdr}
usepackage{sectsty}
usepackage{fontspec}
usepackage{titlesec}

%% Set page size with a wider right margin
geometry{a4paper, total={170mm,257mm}, left=20mm, top=20mm, bottom=20mm, right=50mm}

%% Let's define some colours
definecolor{light}{HTML}{D3D3D3}
definecolor{highlight}{HTML}{800080}
definecolor{dark}{HTML}{330033}

%% Let's add the border on the right hand side 
AddToShipoutPicture{% 
    AtPageLowerLeft{% 
        put(LenToUnit{dimexprpaperwidth-3cm},0){% 
            color{light}rule{3cm}{LenToUnitpaperheight}%
          }%
     }%
     % logo
          }

%% Style the page number
fancypagestyle{mystyle}{
  fancyhf{}
  renewcommandheadrulewidth{0pt}
  fancyfoot[R]{thepage}
  fancyfootoffset{3.5cm}
}
setlength{footskip}{20pt}

%% style the chapter/section fonts
chapterfont{color{dark}fontsize{20}{16.8}selectfont}
sectionfont{color{dark}fontsize{20}{16.8}selectfont}
subsectionfont{color{dark}fontsize{14}{16.8}selectfont}
titleformat{subsection}
  {sffamilyLargebfseries}{thesection}{1em}{}[{titlerule[0.8pt]}]
  
% left align title
makeatletter
renewcommand{maketitle}{bgroupsetlength{parindent}{0pt}
begin{flushleft}
  {sffamilyhugetextbf{MakeUppercase{@title}}} vspace{0.3cm} newline
  {Large {@subtitle}} newline
  @author
end{flushleft}egroup
}
makeatother

%% Use some custom fonts
setsansfont{Ubuntu}[
    Path = fonts/Ubuntu/,
    Scale = 0.9,
    Extension = .ttf,
    UprightFont = *-Regular,
    BoldFont = *-Bold,
    ItalicFont = *-Italic,
    ]
    
setmainfont{keplerstd}[
    Path = fonts/keplerstd/,
    Scale = 0.9,
    Extension = .ttf,
    UprightFont = garr45w,
    BoldFont = bold,
    ItalicFont = italic
    ]

When the dynamic pdf report is tried to be generated the following error occurs;
! LaTeX Error: There's no line here to end.

I appreciate any comments and suggestions to fix the issue. Thank you for your kind attention beforehand.