Package Fancyhdr Warning

Question

Does anyone know how to solve this warning?

The document is composed of several chapters, included through the \input command. The warning does not affect the compilation process of the document (at least for now).

The preambule is as follows:

\documentclass[a4paper, twoside, 12pt]{report}
\usepackage[letterpaper, left=2.9cm, right=2.9cm, top=2.5cm, bottom=2.5cm]{geometry}
\usepackage[spanish]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{hyperref}
\hypersetup{colorlinks=true, urlcolor=violet, linkcolor=Blue, citecolor=Sepia}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage[tight,footnotesize]{subfigure}
\renewcommand{\figurename}{Figura}
\renewcommand{\tablename}{Tabla}
\usepackage{pifont}
\usepackage{enumerate}
\usepackage[usenames,dvipsnames,svgnames,table]{xcolor}
\usepackage[square,sort,comma,numbers]{natbib}
\usepackage{tcolorbox}
\newtcolorbox{mybox}{colback=green!3,colframe=green!75!black}
\newtcolorbox{mybox2}{,colback=blue!3!white,colframe=blue!75!black}
\usepackage{multirow}
\usepackage{cancel}
\renewcommand{\theenumi}{\Roman{enumi}}
\usepackage[version=4]{mhchem} 
\usepackage{tabularx}
\usepackage{supertabular} 
\setlength{\parskip}{5mm}
%\setlength{\parindent}{0cm}
\usepackage{fancyhdr}
\pagestyle{fancy}
\usepackage{appendix}
\newtcolorbox[auto counter, number within=section]{example}[2][]
{colback=green!5!white,colframe=green!75!black,
fonttitle=\bfseries, title=Ejemplo~\thetcbcounter: #2,#1}
\usepackage{wrapfig} % Colocar figuras al lado del texto
\usepackage{float}
\usepackage{titlesec, blindtext, color}
\definecolor{gray75}{gray}{0.75}
\newcommand{\hsp}{\hspace{20pt}}
\titleformat{\chapter}[hang]{\Huge\bfseries}{\thechapter\hsp\textcolor{gray75}{|}\hsp}{0pt}{\Huge\bfseries}
\usepackage{epigraph}