When I previously converted my interior file using Author > Publish > PDF, IngramSpark would reject it.
But I found that if I go to File > Print >Adobe PDF Options and then set “Press Quality,” paper size, embed fonts, and in my case, I want Black & White, that IngramSpark excepted my interior file.
Now I don’t have to move my file from PapyrusAuthor to another program to make a PDF that IS likes.