Simonemonika12345, often the ASIN on Amazon is associated with an ebook/Kindle version of the title involved; Amazon doesn't always include the ISBN of ebooks in their book listings. I was able to find an ISBN for both the print and ebook editions of Wholesome on the South African publisher's website, so I've created records for them in the EYB Library: Wholesome (hardcover) and Wholesome (ebook).
As to why the ISBN's you've tried to import didn't work, were the books published in South Africa? That might have something to do with it; they might not be cataloged on Amazon at all and/or are not coded as food-/drink-related, so Import Books doesn't recognize them as cookbooks.