I use this template. See this question of mine for context.
The document is quite complex, so I'm not sure what to share here in terms of code.
I have this:
\begin{thebibliography}{99}
\bibitem{Bergelson} Bergelson, V., Best, A., and Iosevich (2020). A, Sums of Powers in Large Finite Fields: A Mix of Methods \textit{The American Mathematical Monthly} (2021), 128:8, pp. 701-718.
\end{thebibliography}
However, when I load it, TeXnicCentre says there is an error. When I click of the error, the following shows up:
The problem, of course, seems to be in how I have entered the reference.

natbibneeds the author and year information in the optional argument of\bibitem, see https://tex.stackexchange.com/a/479181/42803 – Andrey L. Mar 06 '24 at 15:24natbib. . . – Shaun Mar 18 '24 at 13:19