If you have accessed this forum then you must already have an Amazon seller account - is it a Business seller account ? It does need to be if you wish to sell your book for profit, and NOT an Individual Seller Account, as that is only for selling off one's own second-hand items. You CAN be on the individual selling PLAN, rather than professional (which is NOT the same as Business.

Is it a book you have written ? If it is, then if you live in UK you must be registered with HMRC as a self-employed sole-trader, and once you have received your UTR you then give that to Amazon to complete your Business Seller Account registration.