Text disappearing if I scale the pdf page

[bfg-coding]

Hello, I've been working on a project where I'm getting a pdf file adding some text to it then having to scale the document to both letter and a4 size. When I do the scale the text I added disappears and I'm not sure if this would be expected or now.

Here's how I'm processing the pdf I get

for (const pdf of songBook.pdfs.sort(
    (a, b) => parseInt(a.songNumber) - parseInt(b.songNumber)
  )) {
    const pdfBytes = await fetchPdf(pdf.url);
    const pdfDoc = await PDFDocument.load(pdfBytes);

    const letterPages = await pdfLetterBook.copyPages(
      pdfDoc,
      pdfDoc.getPageIndices()
    );
    const a4Pages = await pdfA4Book.copyPages(pdfDoc, pdfDoc.getPageIndices());

    letterPages[0] = addSongNumber(
      letterPages[0],
      pdf.songNumber,
      helveticaFont
    );
    a4Pages[0] = addSongNumber(a4Pages[0], pdf.songNumber, helveticaFont);

    letterPages.forEach((page) => {
      pdfLetterBook.addPage(scalePage(page, "letter"));
    });

    a4Pages.forEach((page) => {
      pdfA4Book.addPage(scalePage(page, "a4"));
    });
  }

Here is how I'm adding the song number

function addSongNumber(page: PDFPage, songNumber: string, font: any): PDFPage {
const { height } = page.getSize();
const size = 12;

const textWidth = font.widthOfTextAtSize(songNumber, size);

const x = textWidth;
const y = height - 40;

page.drawText(songNumber, {
  x,
  y,
  size,
  font,
  color: rgb(0, 0, 0), // Black color
});

return page;
}

I've also tried scaling first then adding the song number to the same effect. Has anyone had a similar issue?