Only certain retailers support preordering, namely: Apple, Amazon, Kobo, Google and certain bookstores in the Dilicom France network. For most of these partners, it is mandatory to submit a file (primarily the EPUB file intended for sale) at least two weeks before the sale date. This delay allows them to carry out the various quality control tests before the publication goes on sale and also ensures that they can meet the delivery deadlines for preorders.
In the case of Kobo, the file must be present to launch the preorder.