Why can't I pre-order iPhone 17 as an existing upgrade customer on the Apple Store app?

Hi please can anyone advise why there is no option on the Apple Store app to get ready for the preorder of iphone 17 for existing iphone upgrade customers. The only link for existing upgrade customers is to check eligibility, but that does not allow you to get ready and choose the model, colour, storage that you are looking to upgrade to. It would seem that existing upgrade customers have to wait to 12th Sept to get ready.....can anyone explain this and why? thanks in anticiption, for some help and advice. John

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Original Title: Iphone 17 Pre-order