What type of manuscript should I upload?

Upload a Word document (.docx). It's the format the Interior Formatter reads, and it carries the structure the tool needs (headings, paragraphs, italics, bold).

Whatever you wrote in, you can almost certainly export a DOCX:

• Google Docs → File → Download → Microsoft Word (.docx)
• Apple Pages → File → Export To → Word
• Scrivener → Compile to Word (.docx)

A little prep makes a big difference — see How should I prepare my DOCX before formatting?