Polymorphic callback function not recognized

I am getting the error Uncaught (in promise) TypeError: modNums is not a function. I am following a guide and what I have below is roughly similar to what they did.

Is the issue coming from the fact that I am trying to call the callback inside of a fetch callback? How can I make the modNums function get called? Mind you modNums is just the name of the parameter and there are multiple function that are meant to be accepted for that function value (hence polymorphism).

function updatePageText (chapter, page, modNums) {
  fetch("../../assets/json_files/parsedPages.json")
    .then((Response) => Response.json())
    .then((data) => {
      modNums(chapter, page, data); 

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updatePageText(chapterNum, pageNum, increasePage);