Sorry but if you do not know html and css, and are targeting a Kindle ebook not an epub, and did not read or follow Kindle's Publishing Guidelines, and can not provide a real error message, then we simply can not help.
There could be a million things wrong with your code that Kindle may not like. It could be missing author or title or language metadata, or it uses tags Kindle's do not like. How are we supposed to tell? Sigil is an epub editor and is meant for people who understand html and css and the epub format.
You could try running your epub through the kindlegen program or the KindlePreviewer and perhaps one of those would give you a better error message that might give someone here a hint of what is making KDP unhappy.
FWIW, just importing html into Sigil without any additional work, will never create a perfectly valid epub (no version of Sigil does that).
Last edited by KevinH; 12-25-2020 at 09:51 PM.
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