Reference per chapter biblatex

Question

I'm having a lot of problems with biblatex. I need a reference section per chapter but everytime I compile, I get a bold text with the tag of my reference in the pdf and no reference appears at the end of my chapter.

I attach the main code (yes there are a lot of package and I don't understand if the problem is some incompatibility)

\RequirePackage[hyphens]{url}
\documentclass[a4paper,english,12pt,table]{book}
\usepackage[toc,page]{appendix}
\usepackage{cmap} % makes PDF searchable
\usepackage[english,italian]{babel}
\usepackage[latin9]{inputenc}
\usepackage{lmodern} % Latin Modern font
\usepackage[T1]{fontenc}
\usepackage{textcomp} % needed for fontenc
\usepackage[bookmarksnumbered,final]{easyoutput}
\usepackage{multirow}
\usepackage{layaureo}  
\usepackage{indentfirst}
\usepackage{subfig}
\usepackage{float}
\usepackage{wrapfig}
\usepackage{fancyhdr}
\usepackage{lipsum}
\usepackage{amsmath, bm}
\usepackage{gensymb}
\usepackage{bigints}
\usepackage{caption}
\usepackage{mwe}
\usepackage{amsfonts}
\usepackage{tabu} 
\usepackage{amssymb}
\usepackage[subfigure]{tocloft}
\usepackage{array,amsmath}          
    \newcolumntype{C}{>{\displaystyle}c}
    \newcolumntype{L}{>{\displaystyle}l}
    \newcolumntype{R}{>{\displaystyle}r}
    \newcolumntype{z}{>{{}}c<{{}}} % for mathbin & mathrel
\usepackage[export]{adjustbox}
\usepackage{graphicx}
\usepackage{makecell}
\setcellgapes{5pt}
\usepackage{pdflscape}
\usepackage{emptypage}
\usepackage{cancel}
\usepackage{rotating}
\usepackage{graphicx}
\usepackage{tikz}
\usetikzlibrary{spy}
\usepackage{fancyhdr}
\renewcommand{\headrulewidth}{0.4pt}
\renewcommand{\footrulewidth}{0.4pt}
\usepackage{geometry}
\geometry{text={6.5in,9.5in}
    ,headheight=30pt
}
\setcounter{secnumdepth}{3}
\makeindex
\usepackage[backend=biber,style=authoryear,natbib=true]{biblatex}
\addbibresource{bibliography.bib}
\newenvironment{abstract}
{\cleardoublepage\thispagestyle{empty}
    \vspace{\stretch{1}}
    \begin{center}\textbf{\abstractname}\end{center}\bigskip}
{\par\vspace{\stretch{2}}\cleardoublepage}
\pagestyle{fancy}
\fancyhf{}
\fancyhead[LE]{\includegraphics[height=0.03\textheight]{figure/logo1}}
\fancyhead[RO]{\includegraphics[height=0.03\textheight]{figure/logo2}}
\fancyhead[RE]{\leftmark}
\fancyhead[LO]{\rightmark}
\fancyfoot[RO, LE] {\thepage}
\usepackage{booktabs}
\usepackage{tabularx}
\usepackage{tabulary}
\usepackage{pbox}
\usepackage{tablefootnote}
\usepackage{hyperref}
\makeatletter
\pdfstringdefDisableCommands{\let(\fake@math}
\newcommand\fake@math{}% just for safety
\def\fake@math#1){[math]}
\makeatother
%%% Style chapters
\usepackage[explicit]{titlesec}
\newlength\chapnumb
\setlength\chapnumb{3cm}
\titleformat{\chapter}[block] {
    \normalfont\sffamily}{}{0pt} {
    \parbox[b]{\chapnumb}{
        \fontsize{120}{110}\selectfont\thechapter}
    \parbox[b]{\dimexpr\textwidth-\chapnumb\relax}{
        \raggedleft
        \hfill{\LARGE#1}\
        \rule{\dimexpr\textwidth-\chapnumb\relax}{0.4pt}
    }
}
\titleformat{name=\chapter,numberless}[block]
{\normalfont\sffamily}{}{0pt}
{\parbox[b]{\chapnumb}{%
        \mbox{}}%
    \parbox[b]{\dimexpr\textwidth-\chapnumb\relax}{%
        \raggedleft%
        \hfill{\LARGE#1}\
        \rule{\dimexpr\textwidth-\chapnumb\relax}{0.4pt}}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\title{Title}
\author{Author}
\date{Year}
\begin{document}
    \frenchspacing
    \mainmatter
\cleardoublepage
\selectlanguage{english}
\include{chap1}
\cleardoublepage

\backmatter
\medskip
\end{document}

and the chapt1 for example is like this

\begin{refsection}
\chapter{Tracking Principle}\label{principle} \pagenumbering{arabic}
text text bla bla bla
\printbibliography[heading=subbibintoc]
\end{refsection}

while bibliography.bib is like this

@manual{itu_radio_regulations,
    editor="International Telecommunication Union",
    title = "Radio Regulations Volume 1",
    organization = "International Telecommunication Union",
    address = " Geneva, Switzerland",
    year = "2016"
}

I use Texstudio as editor. Not sure if it is important. I tried to follow a lot of already answered question about this problem but still I cannot solve it. I typically used bibtex but I saw that it is quite hard to have per-chapter bibliography with this so I tried biblatex