It depends how you pronounce "H". If you pronounce it aitch instead of haitch then using "an" in this context is totally correct. https://blog.apastyle.org/apas

It depends how you pronounce "H". If you pronounce it aitch instead of haitch then using "an" in this context is totally correct. https://blog.apastyle.org/apastyle/2012/04/using-a-or-an-with-acronyms-and-abbreviations.html#:~:text=The%20general%20rule%20for%20indefinite,an%20HIV%20patient%20is%20correct https://blog.apastyle.org/apastyle/2012/04/using-a-or-an-wit....