If your book is simple text you can use the free Calibre software to format your book yourself.  It worked fine for me.  If your formatting is more complicated then using a formatting service is probably worth it.

As much as I love Calibre as an ebook library management system, it's conversion plugins can be hit or miss. That's the nature of automated software. Word processing software tends to put a lot of hidden formatting into documents, and it's usually not obvious whether that formatting will break something.

Kovid makes no guarantee that Calibre will create files that will validate or pass Amazon's QA check.

I officially give up on that form plugin. It refuses to work for anyone but me! Email me at info@seampublishing.com and I'll give you details.

I will be reaching out as well.