Undefined control sequence in Bibtex using plain bibliography style

I am trying to compile my references using the plain bibliography style but I keep getting an ‘undefined control sequence’ error.
This is the full error:

    ! Undefined control sequence.
<argument> citeauthoryear 
                           {Riess BOthers {.}}{Riess BOthers {.}}{{APAC...
l.35 ...xpansion of the Universe cite{Riess_1998}
                                                  [1][2], by studying distan...
The control sequence at the end of the top line
of your error message was never def'ed. If you have
misspelled it (e.g., `hobx'), type `I' and the correct
spelling (e.g., `Ihbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

My references.bib file is

@article{Riess_1998,
    doi = {10.1086/300499},
    url = {https://doi.org/10.1086%2F300499},
    year = {1998},
    month = {},
    publisher = {{IOP} Publishing},
    volume = {116},
    number = {3},
    pages = {1009--1038},
    author = {Adam G. Riess and Alexei V. Filippenko and Peter Challis and Alejandro Clocchiatti and Alan Diercks and Peter M. Garnavich and Ron L. Gilliland and Craig J. Hogan and Saurabh Jha and Robert P. Kirshner and B. Leibundgut and M. M. Phillips and David Reiss and Brian P. Schmidt and Robert A. Schommer and R. Chris Smith and J. Spyromilio and Christopher Stubbs and Nicholas B. Suntzeff and John Tonry},
    title = {Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant},
    journal = {The Astronomical Journal},
    abstract = {We present spectral and photometric observations of 10 Type Ia supernovae...}
}

My bbl file is

begin{thebibliography}{}

bibitem [protect citeauthoryear {%
Riess%
 protect BOthers {.}}{%
Riess%
 protect BOthers {.}}{%
{protect APACyear {1998}}%
}]{%
Riess_1998}
APACinsertmetastar {%
Riess_1998}%
begin{APACrefauthors}%
Riess, ABPBI G.%
, Filippenko, ABPBI V.%
, Challis, P.%
, Clocchiatti, A.%
, Diercks, A.%
, Garnavich, PBPBI M.%
BDBL {}Tonry, J.%
end{APACrefauthors}%
unskip
newblock
APACrefYearMonthDay{1998}{}{}.
newblock
{BBOQ}APACrefatitle {Observational Evidence from Supernovae for an
  Accelerating Universe and a Cosmological Constant} {Observational evidence
  from supernovae for an accelerating universe and a cosmological
  constant}.{BBCQ}
newblock
APACjournalVolNumPages{The Astronomical Journal}{116}{3}{1009--1038}.
newblock
begin{APACrefURL} url{https://doi.org/10.1086%2F300499} end{APACrefURL}
newblock
begin{APACrefDOI} doi{10.1086/300499} end{APACrefDOI}
PrintBackRefs{CurrentBib}

end{thebibliography}

My main .tex file is

documentclass{article}
begin{document}
section{Introduction}
In 2011, Perlmutter, Schmidt and Reiss were awarded the Nobel Prize in Physics for their discovery of the accelerating expansion of the Universe cite{Riess_1998}

bibliographystyle{plain}
bibliography{references}

end{document}

Any help would be greatly appreciated! Thank you!