If your Endnotes page isn’t showing up in the right place, here’s how to fix it:
Click on the Formatting Tab and use the three dots next to your theme title to select Edit theme.
Under Notes Settings, change the note settings to Footnotes for PDF and ePub.
Save the theme and return to the Writing Tab.
Allow the Left Navigation pane to refresh without the Endnotes page.
Open the last chapter in the book in the Editor then click on the Formatting Tab.
Switch your Notes Settings back to End of Book and save the theme.
This will add the Endnotes page to the back of your book. Once it's out of the part/volume, you can drag and drop it to the location you would like it to appear.