How to use APA6 style in Elsevier's cas-dc.cls class file

Question

Last week I have submitted my manuscript to the ESWA (Expert Systems with Applications), but two days ago they sent an email about my citation format. Here is the mail:

Please note that all paper submissions must completely comply with ESWA reference style and reference list (see details at https://www.elsevier.com/journals/expert-systems-with-applications/0957-4174/guide-for-authors) prior to a rigorous peer review process.

Reference Style:

Citations in the text should follow the referencing style used by the American Psychological Association. You are referred to the Publication Manual of the American Psychological Association, Sixth Edition, ISBN 978-1-4338-0561-5. APA’s in-text citations require the author’s last name and the year of publication. You should cite publications in the text, for example, (Smith, 2020). However, you should not use [Smith, 2020]. Note: There should be no [1], [2], [3], etc in your manuscript.

Reference List:

References should be arranged first alphabetically by the surname of the first author followed by initials of the author’s given name, and then further sorted chronologically if necessary. More than one reference from the same author(s) in the same year must be identified by the letters 'a', 'b', 'c', etc., placed after the year of publication. For example, Van der Geer, J., Hanraads, J. A. J., & Lupton, R. A. (2010). The art of writing a scientific article. Journal of Scientific Communications, 163, 51–59. https://doi.org/10.1016/j.Sc.2010.00372. Note: There should be no [1], [2], [3], etc in your references list.

You can see both reference style and reference list in a published ESWA Open Access article available at https://www.sciencedirect.com/science/article/pii/S0957417420306138

So, I have been trying to use APA6 bibliography style in my manuscript last two days, (cas-dc.cls) but nothing worked for me so far:

\documentclass[a4paper,fleqn]{cas-dc}
\begin{filecontents}{\jobname.bib} 
@article{Ha89,
Author = {Peter M. Haas},
Date-Added = {2017-02-06 21:15:57 +0000},
Date-Modified = {2017-02-06 21:45:06 +0000},
Journal = {International Organization},
urldate = {2010-02-03T12:54:00},
Number = {3},
Pages = {377-403},
Publisher = {Peter Haas},
Read = {0},
Title = {Do regimes matter? {Epistemic} communities and {Mediterranean} pollution control},
url = {http://www.jstor.org/stable/2706652},
Volume = {43},
Year = {1989}}
\end{filecontents}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage[ruled,vlined]{algorithm2e}
\usepackage{algorithmic}
\usepackage{array}
%\usepackage[authoryear]{natbib}    
%\usepackage{natbib}
%\usepackage[natbibapa]{apacite}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%Below part is suggested at https://tex.stackexchange.com/a/352816/68836 
%It works actually but prints weird things on first page like "=0pt [],n;"
%These weird things disappers only if I import natbib package.
%But this time, citations and re. list becomes numerical whatever I do.
\usepackage[style=apa]{biblatex}
\defbibheading{bibliography}[\bibname]{\section{#1}}
\addbibresource{cas-refs.bib}
\usepackage{csquotes}
\usepackage{hyperref}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
This is an in text citation: \textcite{Ha89}.  This is a parenthetical one: \parencite{Ha89} for biblatex suggested in https://tex.stackexchange.com/a/352816/68836
Also tried \cite{Ha89}, \citep{Ha89}, \citet{Ha89} etc. nothing worked.
%\bibliographystyle{apacite}
%\bibliographystyle{elsarticle-num} 
%\bibliographystyle{cas-model2-names}%\biboptions{authoryear}
%\bibliographystyle{model5-names}
%\bibliographystyle{apa}
%\bibliography{cas-refs}
\printbibliography %for the biblatex
\end{document}

The cas-dc.cls can be found here: https://www.ctan.org/tex-archive/macros/latex/contrib/els-cas-templates

In cas-dc's documentation, it suggest to use elsarticle-num.bst for numerical or model2-names.bst for alphabetical. I used second one with \usepackage[authoryear]{natbib}, still prints [num] format with cite, citep, citet, citealt

I have tried every possible pairing style (I mean \ usepackage{} and \bibliographystyle{}) with all possible \cite*** commands. Nothing worked except the biblatex but as I said earlier, it prints weird thing on the first page.

Can someone help me?

Answer 1

The class cannot be used with biblatex because although it doesn't load the natbib package, it uses a macro from natbib (\bibsep). So this means that you need to use the apacite package with the [natbibapa] option to get APA 6 style:

\documentclass[a4paper,fleqn]{cas-dc}
\begin{filecontents}{\jobname.bib} 
@article{Ha89,
Author = {Peter M. Haas},
Date-Added = {2017-02-06 21:15:57 +0000},
Date-Modified = {2017-02-06 21:45:06 +0000},
Journal = {International Organization},
urldate = {2010-02-03T12:54:00},
Number = {3},
Pages = {377-403},
Publisher = {Peter Haas},
Read = {0},
Title = {Do regimes matter? {Epistemic} communities and {Mediterranean} pollution control},
url = {http://www.jstor.org/stable/2706652},
Volume = {43},
Year = {1989}}
\end{filecontents}
\usepackage[english]{babel}
\usepackage[natbibapa]{apacite}
\bibliographystyle{apacite}
\usepackage{csquotes}
\usepackage{hyperref}
\title{A title}
\author{an Author}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
\maketitle
This is an in text citation: \citet{Ha89}.  This is a parenthetical one: \citep{Ha89} for biblatex suggested in https://tex.stackexchange.com/a/352816/68836
Also tried \cite{Ha89}, \citep{Ha89}, \citet{Ha89} etc. nothing worked.
\bibliography{\jobname}
\end{document}