Problem with citing authors - showing (author ? )

Question

I'm trying to cite authors in an overleaf project. I would like for it to be on this format:

However, I'm getting this:

Here is my overleaf code:

\documentclass[pdftex,10pt,b5paper,twoside]{book}
\usepackage[utf8]{inputenc}
\usepackage{natbib}
\def\biblio{\bibliographystyle{unsrt}\bibliography{references}}

\begin{document}
\def\biblio{references} % For making bibliography working with subfiles, prints at end of each subfile
% \maketitle
Trying to cite this author \citeauthor{fossen2011} \\
How about this \citet{fossen2011} \\ 
Alternative workaround method: \cite[Fossen (2011)]{fossen2011} 


\bibliographystyle{unsrt}
% \bibliographystyle{elsarticle-harv}
\bibliography{references}

\end{document}

And my reference.bib file:

<bibtex>

@book{fossen2011,
    author = {Fossen, T. I.},
    title = {Handbook of Marine Craft Hydrodynamics and Motion Control},
    publisher = {John Wiley \& Sons, Ltd},
    year = {2011},
    address = {West Sussex, United Kingdom}
}

Does anyone know how to get a proper citation? Appriciate any help!

Answer 1

in my point of view it has something to do with natbib and the

\bibliographystyle{unsrt} 

You can use

\bibliographystyle{plainnat} 

which is natbibs own plain version.