Handed my Word file over to Nextzen Book Publisher to get it formatted for print and Kindle. I’d been trying to do it myself on Word, but the page numbers kept messing up and the indented quotes looked terrible on the previewer.
Their layout person went in and cleaned up the whole file. They fixed the mirror margins so the text doesn't run into the spine, and built the ePub so the chapter headings actually stay attached to the paragraphs below them on phone screens. They sent a draft back for me to check, and I asked them to pull back the line spacing a bit because it looked a little too spread out. They fixed it that afternoon.
Both files uploaded to KDP without throwing any of those annoying formatting error flags. Saved me a massive headache trying to fix margin errors on my own.