[Tex/LaTex] BibTex and Overleaf. Citations not working

bibliographiesbibtexoverleaf

I am trying to add a bibliography to my Overleaf latex document and for that I am using BibTex.

I downloaded a .bib file from Zotero which automatically generates them for you and imported it into my Overleaf project. The file is named security_policy.bib. Then I added the \bibliogray and \bibliography tags at the end of the document (before \end{document}):

\backmatter
\bibliographystyle{hispa}
\bibliography{security_policy.bib}

I am trying to cite ISO/IEC 27002 which is referenced by the bib file as "27_iso/iec_2008". As I start typing \cite, the reference "27_iso/iec_2008" automatically pops up, which means the bibliography has been correctly imported.

However, when the PDF document is generated (which according to the official Overleaf examples and guides automatically runs bibtex therefore creating the bibliography references), the cite is missing (it is showing [?] instead).

What should I do to fix this issue?