Change citation system to APA 7th edition

Question

I've been trying to change the citation system to APA, but when I use "apacite" it creates an error, would you mind helping me out? Also, I'd like to use the APA system in Spanish. How do I implement that language here?

\documentclass[11pt, english, singlespacing, headsepline]{MastersDoctoralThesis} 
\usepackage[backend=bibtex,style=authoryear,natbib=true]{biblatex}
% Use the bibtex backend with the authoryear citation style (which resembles APA)
\addbibresource{example.bib} % The filename of the bibliography
\usepackage[autostyle=true]{csquotes} % Required to generate language-dependent quotes
%BIBLIOGRAPHY
\printbibliography[heading=bibintoc]
\end{document}

UPDATE: Yeah, seems I didn't explain myself correctly. I'm using "english" because that's a template. I didn't make the file, I'm just editing it. I tried using "spanish" but it created a conflict. I need to keep the format of the template, that's why I shouldn't change it to {article}.

This is the {MasterDoctoralThesis}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Masters/Doctoral Thesis 
% Class File
% Version 1.6 (27/8/17)
%
% This class was downloaded from:
% http://www.LaTeXTemplates.com
%
% Authors:
% Vel (vel@latextemplates.com)
% Johannes Böttcher
%
% Notes:
% 1) This class file defines the structure and layout of the template file (main.tex).
% 2) It has been written in such a way that under most circumstances you should not need
% to edit it; updating it to a newer version will be harder. If you do make changes, please change the name of
% the file and add comments to make your changes more visible.
%
% Class license:
% LPPL v1.3c (http://www.latex-project.org/lppl)
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%----------------------------------------------------------------------------------------
%   CLASS DEFINITION AND PARAMETERS
%----------------------------------------------------------------------------------------
\NeedsTeXFormat{LaTeX2e}[1996/12/01]
\newcommand{\classname}{MastersDoctoralThesis}
\ProvidesClass{\classname}[2017/08/27 v1.6 LaTeXTemplates.com]
\providecommand{\baseclass}{book}
\RequirePackage{etoolbox}
\RequirePackage{xparse}
\newbool{nolistspace}
\newbool{chapteroneline}
\newbool{listtoc}
\newbool{toctoc}
\newbool{parskip}
\newbool{hyperrefsupport}
\booltrue{hyperrefsupport}
\newbool{headsepline}
\newbool{consistentlayout}
\DeclareOption{nohyperref}{\boolfalse{hyperrefsupport}}
\DeclareOption{nolistspacing}{\booltrue{nolistspace}}
\DeclareOption{liststotoc}{\booltrue{listtoc}}
\DeclareOption{chapterinoneline}{\booltrue{chapteroneline}}
\DeclareOption{toctotoc}{\booltrue{toctoc}}
\DeclareOption{parskip}{\booltrue{parskip}}
\DeclareOption{headsepline}{\booltrue{headsepline}}
\DeclareOption{consistentlayout}{\booltrue{consistentlayout}}
\DeclareOption*{\PassOptionsToClass{\CurrentOption}{\baseclass}}
\ProcessOptions\relax
\LoadClass{\baseclass}
%  Simple interface for the user  to customize the chapter titles 
\ProvideDocumentCommand{\abovechapterskip}{}{\vspace{20pt}}
\ProvideDocumentCommand{\chapterbelowskip}{}{\vspace{40pt}}
\ProvideDocumentCommand{\chapterinbetweenskip}{}{\vspace*{20pt}}
\ProvideDocumentCommand{\autodot}{}{}
\ProvideDocumentCommand{\mdtChapapp}{}{}
\ProvideDocumentCommand{\chapteralign}{}{\raggedright}
\ProvideDocumentCommand{\chapterfont}{}{\Huge\bfseries}
\ProvideDocumentCommand{\chapterprefixfont}{}{\LARGE\bfseries}
\DeclareDocumentCommand{@makechapterhead}{ m }{%
    \abovechapterskip
    {\parindent \z@ \chapteralign \normalfont
        \ifnum \c@secnumdepth >\m@ne
        \if@mainmatter
        \ifbool{chapteroneline}{%
            \chapterfont \mdtChapapp\thechapter\autodot\enspace
        }{%
            \chapterprefixfont @chapapp\space \thechapter
            \par\nobreak
            \chapterinbetweenskip
        }%
        \fi
        \fi
        \interlinepenalty@M%
        \chapterfont #1\par\nobreak
        \chapterbelowskip
    }
    \thispagestyle{\chapter@p@gestyle}
}
\def@makeschapterhead#1{%
    \abovechapterskip
    {\parindent \z@ \chapteralign
        \normalfont
        \interlinepenalty@M
        \chapterfont  #1\par\nobreak
        \chapterbelowskip
    }
    \thispagestyle{\chapter@p@gestyle}
}
% Addchap provides unnumbered chapters with an entry in the table of contents as well as an updated header
\ProvideDocumentCommand{\addchap}{ s o m }{%
    \chapter*{#3}%
    \markboth{}{}%
    \IfBooleanTF{#1}{%
    }{%
        \IfNoValueTF{#2}{%
            \addchaptertocentry{#3}%
            \markboth{\MakeMarkcase{#3}}{\MakeMarkcase{#3}}%
        }{%
            \addchaptertocentry{#2}%
            \markboth{\MakeMarkcase{#2}}{\MakeMarkcase{#2}}%
        }%
    }%
}%
\ProvideDocumentCommand{\addsec}{ s o m }{%
    \section*{#3}%
    \markright{}%
    \IfBooleanTF{#1}{%
    }{%
        \IfNoValueTF{#2}{%
            \addcontentsline{toc}{section}{#3}%
            \markright{\MakeMarkcase{#3}}%%
        }{%
            \addcontentsline{toc}{section}{#2}%
            \markright{\MakeMarkcase{#2}}%
        }%
    }%
}%
%----------------------------------------------------------------------------------------
%   CLASS OPTIONS
%----------------------------------------------------------------------------------------
\ifbool{parskip}{\RequirePackage{parskip}} % If the parskip option is passed to the class, require the parskip package
\ifbool{listtoc}{% If the liststotoc option has been passed to the class, add the lists to the table of contents
    \patchcmd{\listoftables}{@starttoc{lot}}{%
        \addchaptertocentry{\listtablename}@starttoc{lot}%
    }{}{}%
    \patchcmd{\listoffigures}{@starttoc{lof}}{%
        \addchaptertocentry{\listfigurename}@starttoc{lof}%
    }{}{}%
}
\ifbool{toctoc}{% If the toctotoc options has been passed to the class, add the table of contents to the table of contents
    \patchcmd{\tableofcontents}{@starttoc{toc}%
}{%
    \addchaptertocentry{\contentsname}@starttoc{toc}}{}{}%
}
\patchcmd{\tableofcontents}{\MakeUppercase}{\MakeMarkcase}{}{}
\patchcmd{\tableofcontents}{\MakeUppercase}{\MakeMarkcase}{}{}
\patchcmd{\listoffigures}{\MakeUppercase}{\MakeMarkcase}{}{}
\patchcmd{\listoffigures}{\MakeUppercase}{\MakeMarkcase}{}{}
\patchcmd{\listoftables}{\MakeUppercase}{\MakeMarkcase}{}{}
\patchcmd{\listoftables}{\MakeUppercase}{\MakeMarkcase}{}{}
% If the option `nolistspacing' is given, the spacing in the different lists is reduced to single spacing. This option is only useful, if the spacing of the document has been changed to onehalfspacing or doublespacing.
\ifbool{nolistspace}{
    \patchcmd{\listoffigures}{%
        @starttoc{lof}
    }{%
        \begingroup%
        \singlespace@starttoc{lof}\endgroup%
    }{}{}%
    \patchcmd{\listoftables}{%
        @starttoc{lot}
    }{%
        \begingroup%
        \singlespace@starttoc{lot}\endgroup%
    }{}{}%
    \patchcmd{\tableofcontents}{%
        @starttoc{toc}
    }{%
        \begingroup%
        \singlespace@starttoc{toc}\endgroup%
    }{}{}%
}{}
%----------------------------------------------------------------------------------------
%   REQUIRED PACKAGES
%----------------------------------------------------------------------------------------
\RequirePackage{babel} % Required for automatically changing names of document elements to languages besides english
\RequirePackage{scrbase} % Required for handling language-dependent names of sections/document elements
\RequirePackage{scrhack} % Loads fixes for various packages
\RequirePackage{setspace} % Required for changing line spacing
\RequirePackage{longtable} % Required for tables that span multiple pages (used in the symbols, abbreviations and physical constants pages)
\RequirePackage{siunitx} % Required for \SI commands
\RequirePackage{graphicx} % Required to include images
\graphicspath{{Figures/}{./}} % Specifies where to look for included images
\RequirePackage{booktabs} % Required for better table rules
\RequirePackage{caption} % Required for customising the captions
\captionsetup{justification=centerlast,font=small,labelfont=sc,margin=50pt}
%----------------------------------------------------------------------------------------
%   DEFINE CUSTOM THESIS INFORMATION COMMANDS
%----------------------------------------------------------------------------------------
\NewDocumentCommand{\thesistitle} { o m }{%
 \IfValueTF{#1}{\def\shorttitle{#1}}{\def\shorttitle{#2}}%
 \def@title{#2}%
 \def\ttitle{#2}%
}
\DeclareDocumentCommand{\author}{m}{\newcommand{\authorname}{#1}\renewcommand{@author}{#1}}
\NewDocumentCommand{\supervisor}{m}{\newcommand{\supname}{#1}}
\NewDocumentCommand{\examiner}{m}{\newcommand{\examname}{#1}}
\NewDocumentCommand{\degree}{m}{\newcommand{\degreename}{#1}}
\NewDocumentCommand{\addresses}{m}{\newcommand{\addressname}{#1}}
\NewDocumentCommand{\university}{m}{\newcommand{\univname}{#1}}
\NewDocumentCommand{\department}{m}{\newcommand{\deptname}{#1}}
\NewDocumentCommand{\group}{m}{\newcommand{\groupname}{#1}}
\NewDocumentCommand{\faculty}{m}{\newcommand{\facname}{#1}}
\NewDocumentCommand{\subject}{m}{\newcommand{\subjectname}{#1}}
\NewDocumentCommand{\keywords}{m}{\newcommand{\keywordnames}{#1}}
\newcommand{\checktoopen}{% New command to move content to the next page which prints to the next odd page if twosided mode is active

    \if@openright\cleardoublepage\else\clearpage\fi
    \ifdef{\phantomsection}{\phantomsection}{}% The \phantomsection command is necessary for hyperref to jump to the correct page
}
\NewDocumentCommand{\bhrule}{}{\typeout{--------------------}}
\NewDocumentCommand{\tttypeout}{m}{\bhrule\typeout{\space #1}\bhrule}
\newcommand{\HRule}{\rule{.9\linewidth}{.6pt}} % New command to make the lines in the title page
\newcommand{\decoRule}{\rule{.8\textwidth}{.4pt}} % New command for a rule to be used under figures
\setcounter{tocdepth}{3} % The depth to which the document sections are printed to the table of contents
\ProvideDocumentCommand{\addchaptertocentry}{ m }{%
    \addcontentsline{toc}{chapter}{#1}%
}
%----------------------------------------------------------------------------------------
%   COLOURS
%----------------------------------------------------------------------------------------
\usepackage{xcolor} % Required for specifying custom colours
\colorlet{mdtRed}{red!50!black}
%----------------------------------------------------------------------------------------
%   MARGINS
%----------------------------------------------------------------------------------------
\RequirePackage{geometry}
\geometry{
    headheight=4ex,
    includehead,
    includefoot
}
\raggedbottom
%----------------------------------------------------------------------------------------
%   PENALTIES
%----------------------------------------------------------------------------------------
\doublehyphendemerits=10000 % No consecutive line hyphens
\brokenpenalty=10000 % No broken words across columns/pages
\widowpenalty=9999 % Almost no widows at bottom of page
\clubpenalty=9999 % Almost no orphans at top of page
\interfootnotelinepenalty=9999 % Almost never break footnotes
%----------------------------------------------------------------------------------------
%   HEADERS AND FOOTERS
%----------------------------------------------------------------------------------------
\RequirePackage[markcase=used]{scrlayer-scrpage}
\providepairofpagestyles{thesisSimple}{%
    \clearpairofpagestyles%
    \automark[chapter]{chapter}
    \ihead{\headmark}% Inner header
    \ohead[\pagemark]{\pagemark}% Outer header
}
\ifoot{}% Inner footer
\ofoot{}% Outer footer
\pagestyle{thesisSimple}
\providepairofpagestyles[thesisSimple]{thesis}{%
    \automark*[section]{}%
}
\providepairofpagestyles[thesisSimple]{review}{%
    \ofoot[\shorttitle/\authorname]{\shorttitle/\authorname}
    \ifoot[\today]{\today}
}
\pagestyle{thesis}
\ifbool{headsepline}{\KOMAoption{headsepline}{true}}{}
\PreventPackageFromLoading[\ClassError{\classname}{Package fancyhdr' is incompatible\MessageBreak with this class}{The pagesyles are defined using packagescrlayer-scrpage', please consult the\MessageBreak 
KOMA-script documentation for details.}]{fancyhdr}
\newcommand{\blank@p@gestyle}{empty}
\newcommand{\chapter@p@gestyle}{plain}
\NewDocumentCommand{\blankpagestyle}{ m }{%
    \ClassWarning{\classname}{\string\blankpagestyle\space is
    obsolete,\MessageBreak use \string\setblankpagestyle \space  instead}\renewcommand{\blank@p@gestyle}{}{#1}
}
\NewDocumentCommand{\setblankpagestyle}{ m }{\renewcommand{\blank@p@gestyle}{#1}}
\NewDocumentCommand{\setchapterpagestyle}{ m }{\renewcommand{\chapter@p@gestyle}{#1}}
\DeclareDocumentCommand\cleardoublepage{}{\clearpage\if@twoside \ifodd\c@page\else
    \hbox{}
    \thispagestyle{\blank@p@gestyle}
    \newpage
    \if@twocolumn\hbox{}\newpage\fi\fi\fi%
}
%----------------------------------------------------------------------------------------
%   ABBREVIATIONS PAGE DESIGN
%----------------------------------------------------------------------------------------
\newcommand{\abbrevname}{List of Abbreviations}
\providecaptionname{english,british,american}{\abbrevname}{List of Abbreviations}
\providecaptionname{ngerman,german,austrian,naustrian}{\abbrevname}{Abk"urzungsverzeichnis}
\NewDocumentEnvironment{abbreviations}{ m }{%
    \ifbool{nolistspace}{\begingroup\singlespacing}{}
    \ifbool{listtoc}{\addchap{\abbrevname}}{\addchap*{\abbrevname}}
    \begin{longtable}{#1}
    }{%
    \end{longtable}
    \addtocounter{table}{-1}% Don't count this table as one of the document tables
    \ifbool{nolistspace}{\endgroup}{}
}
%----------------------------------------------------------------------------------------
%   ABSTRACT PAGE DESIGN
%----------------------------------------------------------------------------------------
\DeclareDocumentCommand{\abstractauthorfont}{}{}
\DeclareDocumentCommand{\abstracttitlefont}{}{}
\newcommand{\byname}{by}
\newcommand{\abstractname}{Abstract}
\providecaptionname{german,ngerman,austrian,naustrian}{\byname}{von}
\providecaptionname{american,australian,british,canadian,english,newzealand,UKenglish,USenglish}{\byname}{by}
\ifbool{consistentlayout}{
    \DeclareDocumentEnvironment{abstract}{ O{} }{%
        \addchap*{\abstractname}%
        {\chapteralign\normalsize\abstractauthorfont \authorname \par}% Author name
        \vspace{\baselineskip}
        {\chapteralign\parbox{.7\linewidth}{\chapteralign\normalsize\itshape\abstracttitlefont@title}\par}% Thesis title
        \bigskip\noindent\ignorespaces
    }%
    {}%end alt-abstract
}{%
    \DeclareDocumentEnvironment{abstract}{ O{\null\vfill} }{
        \checktoopen
        \tttypeout{\abstractname}
        #1%added to be able to have abstract more than one page long
        \thispagestyle{plain}
        \begin{center}
            {\normalsize \MakeUppercase{\univname} \par}% University name in capitals
            \bigskip
            {\huge\textit{\abstractname} \par}
            \bigskip
            {\normalsize \facname \par}% Faculty name
            {\normalsize \deptname \par}% Department name
            \bigskip
            {\normalsize \degreename\par}% Degree name
            \bigskip
            {\normalsize\bfseries @title \par}% Thesis title
            \medskip
            {\normalsize \byname{} \authorname \par}% Author name
            \bigskip
        \end{center}
    }
    {
        \vfill\null
    }
}
\DeclareDocumentEnvironment{extraAbstract}{ O{\null\vfill} }{
    \checktoopen
    \tttypeout{\abstractname}
    #1%added to be able to have abstract more than one page long
    \thispagestyle{empty}
    \begin{center}
        {\normalsize \MakeUppercase{\univname} \par}% University name in capitals
        \bigskip
        {\huge\textit{\abstractname} \par}
        \bigskip
        {\normalsize \facname \par}% Faculty name
        {\normalsize \deptname \par}% Department name
        \bigskip
        {\normalsize \degreename\par}% Degree name
        \bigskip
        {\normalsize\bfseries @title \par}% Thesis title
        \medskip
        {\normalsize \byname{} \authorname \par}% Author name
        \bigskip
    \end{center}
}
{
    \vfill\null
}
%----------------------------------------------------------------------------------------
%   ACKNOWLEDGEMENTS PAGE DESIGN
%----------------------------------------------------------------------------------------
\usepackage{xcolor}
\colorlet{mdtRed}{red!50!black}
\newcommand{\acknowledgementname}{Acknowledgements}
\providecaptionname{american,australian,british,canadian,english,newzealand,UKenglish,USenglish} {\acknowledgementname}{Acknowledgements} % Acknowledgement text for English countries
\providecaptionname{german,ngerman,austrian,naustrian}{\acknowledgementname}{Danksagung} % Acknowledgement text for Germanic countries
\ifbool{consistentlayout}{
    \DeclareDocumentEnvironment{acknowledgements}{}{%
        \tttypeout{\acknowledgementname}
        \addchap*{\acknowledgementname}
    }
}
{
    \DeclareDocumentEnvironment{acknowledgements}{}{%
        \checktoopen
        \tttypeout{\acknowledgementname}
        \thispagestyle{plain}
        \begin{center}{\huge\textit{\acknowledgementname}\par}\end{center}
    }
    {
        \vfil\vfil\null
    }
}
%----------------------------------------------------------------------------------------
%   DECLARATION PAGE DESIGN
%----------------------------------------------------------------------------------------
\newcommand{\authorshipname}{Declaration of Authorship}
\providecaptionname{american,australian,british,canadian,english,newzealand,UKenglish,USenglish}{\authorshipname}{Declaration of Authorship} % Declaration of Authorship text for English countries
\providecaptionname{german,ngerman,austrian,naustrian}{\authorshipname}{Eidesstattliche Erkl"arung} % Declaration of Authorship text for Germanic countries
\ifbool{consistentlayout}{
    \DeclareDocumentEnvironment{declaration}{}{
        \addchap*{\authorshipname}
        }{}%
}{
    \DeclareDocumentEnvironment{declaration}{}{
        \checktoopen
        \tttypeout{\authorshipname}
        \thispagestyle{plain}
        \null\vfil
        {\noindent\huge\bfseries\authorshipname\par\vspace{10pt}}
    }{}
}
%----------------------------------------------------------------------------------------
%   DEDICATION PAGE DESIGN
%----------------------------------------------------------------------------------------
\ifbool{consistentlayout}{
    \DeclareDocumentCommand{\dedicatory}{
        m O{\vspace*{.7\textheight} }  }{
            \checktoopen\tttypeout{Dedicatory}
            \markboth{}{}
            #2
            {\hfill\parbox{.4\textwidth}{\flushright#1\par}}
        }
}{
    \newcommand\dedicatory[1]{
        \checktoopen
        \tttypeout{Dedicatory}
        \null\vfil
        \thispagestyle{plain}
        \begin{center}{\Large\slshape #1}\end{center}
        \vfil\null
    }
}
%----------------------------------------------------------------------------------------
%   PHYSICAL CONSTANTS PAGE DESIGN
%----------------------------------------------------------------------------------------
\newcommand{\constantsname}{Physical Constants}
\providecaptionname{english,british,american}{\constantsname}{Physical Constants}
\providecaptionname{ngerman,german,austrian,naustrian}{\constantsname}{Physikalische Konstanten}
\NewDocumentEnvironment{constants}{ m }{%
    \ifbool{nolistspace}{\begingroup\singlespacing}{}
    \ifbool{listtoc}{\addchap{\constantsname}}{\addchap*{\constantsname}}
    \begin{longtable}{#1}
    }{%
    \end{longtable}
    \addtocounter{table}{-1}% Don't count this table as one of the document tables
    \ifbool{nolistspace}{\endgroup}{}
}
%----------------------------------------------------------------------------------------
%   SYMBOLS PAGE DESIGN
%----------------------------------------------------------------------------------------
\newcommand{\symbolsname}{List of Symbols}
\providecaptionname{english,british,american}{\symbolsname}{List of Symbols}
\providecaptionname{ngerman,german,austrian,naustrian}{\symbolsname}{Symbolverzeichnis}
\NewDocumentEnvironment{symbols}{ m }{%
    \ifbool{nolistspace}{\begingroup\singlespacing}{}
    \ifbool{listtoc}{\addchap{\symbolsname}}{\addchap*{\symbolsname}}
    \begin{longtable}{#1}
    }{%
    \end{longtable}
    \addtocounter{table}{-1}% Don't count this table as one of the document tables
    \ifbool{nolistspace}{\endgroup}{}
}
%----------------------------------------------------------------------------------------
\ifbool{hyperrefsupport}{% If the nohyperref class option has not been specified
\AtEndPreamble{\RequirePackage{hyperref}
\hypersetup{pdfpagemode={UseOutlines},
bookmarksopen=true,
bookmarksopenlevel=0,
hypertexnames=false,
colorlinks=true,% Set to false to disable coloring links
citecolor=magenta,% The color of citations
linkcolor=red,% The color of references to document elements (sections, figures, etc)
urlcolor=mdtRed,% The color of hyperlinks (URLs)
pdfstartview={FitV},
unicode,
breaklinks=true,
}
\pdfstringdefDisableCommands{% If there is an explicit linebreak in a section heading (or anything printed to the pdf-bookmarks), it is replaced by a space
    \let\\space%
}
    }
}{%nothing
}
%----------------------------------------------------------------------------------------
\endinput
% lazyLizardTracer

Answer 1

Starting point. Also, see Is there a way to apply Apa 7th references and citation style in latex?.

\documentclass[spanish]{article}
\usepackage[style=apa, backend=biber]{biblatex}
\addbibresource{\jobname.bib}
\usepackage{csquotes}
\usepackage{babel}
\begin{filecontents}{\jobname.bib}
@book{key,
  author = {Author, A.},
  year = {2001},
  title = {Title},
  publisher = {Publisher},
}
\end{filecontents}
\begin{document}
\cite{key}
\printbibliography
\end{document}