Change font of bibliography content not Heading

I have to write a document with the following characteristics:

1. US letter size paper
2. Two column with space between columns of 9.9mm
3. Left and right margins of 23mm
4. Top margin of 30mm and bottom of 35mm
5. The "Resumen", Abstact and Introduction has to be of size 12, bold and in the center (of the column they belong)
6. The following sections has to be of size 10, bold, left aligned
7. The subsections has to be of size 10, italic and left aligned
8. The size of the actual text has to be 9
9. The bibliography content (not heading) has to be of size 8

So far I was able to do 1-7 requirements but I can’t do the 8 step. Here is my solution

documentclass[10pt]{article}
usepackage[T1]{fontenc}
usepackage[utf8]{inputenc}
usepackage[spanish]{babel}
usepackage{titlesec}
usepackage{apacite}
usepackage{blindtext}
usepackage{multicol}

titleformat{section}[hang]{centeringlargebfseries}{}{0pt}{}
renewcommand{thesection}{}
renewcommand{thesubsection}{normalsizearabic{subsection}}
titleformat{subsubsection}{normalsizeem}{thesubsubsection}{1em}{}

title{draft}
author{Luis}

begin{document}
maketitle
begin{multicols}{2}

small 
section{Resumen}
blindtext

section{Abstract}
blindtext

section{Introducción}
blindtext

subsection{a ver}
blindtext

subsubsection{a ver dos}
blindtext

end{multicols}

nocite{Gould}
bibliographystyle{apacite}
{footnotesize
bibliography{mybib}}

end{document}

I choose the font of size 10pt because here say the following:

• small is 9pt
• large is 12pt
• footnotesize is 8pt

I use the package geometry to defined the papaer size of my document as well as the margins. This solves points 1, 3 and 4. The package multicol is used to make the document two column.

The titleformat{...} makes the sections numberless but the subsection and subsubsection keep their numbering. This solves points 5, 6 and 7.

To make normal text of size 9, I use the command small inside the multicols enviroment, and I think this solves point 8.

But I can’t make the text in my bibliography to be of size 8pt, that is the size of footnotesize. The file mybib.bib has the following entrie:

@book{Gould,
author="Gould, S",
title="Russian for the mathematician",
year="1972",
address="NY, US",
publisher="Springer-Verlag"}

I have read some questions and their answers but so far none work for me, how can I mak it?

*NOTE If you compile the code, you will find out that blindtext doesn’t work in spanish, but this error does not affect the formating

newcommandsmall{%
   @setfontsizesmall@viiipt@ixpt%
   abovedisplayskip 5p@ @plus2p@ @minus2p@
   abovedisplayshortskip z@ @plus1p@
   belowdisplayshortskip 3p@ @plusp@ @minus2p@
   def@listi{leftmarginleftmargini
               topsep 3p@ @plusp@ @minusp@
               parsep 2p@ @plusp@ @minusp@
               itemsep parsep}%
   belowdisplayskip abovedisplayskip
}

documentclass[9pt]{article}
usepackage[T1]{fontenc}
usepackage[utf8]{inputenc}
usepackage[spanish]{babel}
usepackage{titlesec}
usepackage{apacite}
usepackage{blindtext}
usepackage{multicol}

titleformat{section}[hang]{centeringlargebfseries}{}{0pt}{}
renewcommand{thesection}{}
renewcommand{thesubsection}{normalsizearabic{subsection}}
titleformat{subsubsection}{normalsizeem}{thesubsubsection}{1em}{}
renewcommand{bibliographytypesize}{small}

title{draft}
author{Luis}

begin{document}
    maketitle
    begin{multicols}{2}
        
        small 
        section{Resumen}
        blindtext
        
        section{Abstract}
        blindtext
        
        section{Introducción}
        blindtext
        
        subsection{a ver}
        blindtext
        
        subsubsection{a ver dos}
        blindtext
        
    end{multicols}
    
    nocite{Gould}
    bibliographystyle{apacite}
    {footnotesize
        bibliography{mybib}}
    
end{document}

renewcommand{bibliographytypesize}{footnotesize}