What is the difference between an ASIN and an ISBN?

ASIN is amazon unique identifier  and ISBN is international Standard of book numbers unique identifier. You can buy ISBN from https://codesforamazon.com/product-category/barcodes/isbn-numbers-for-books/

whereas you cannot buy any ASIN to add products in amazon.

When you create a listing with the help of any barcode EAN UPC or ISBN then it issue an ASIN for that product page which is amazon property.

Lastly if you have already same product listed then you can use same listing ASIN and jump on the same listing where you can use the option to sell yours in amazon product page or add a new product and search with asin or isbn or your product then sell yours when your offer will be active ASIN will remain same for all sellers and product page will remain same for your book. but if your product in not already selling then buy new cheap isbn to list you item at amazon and start selling.

Hope it will help you to find the solution and use of both easily, Solution is to launch books under your isbn so you will have some priorities over buy box from others and have more sales.

https://codesforamazon.com/product-category/barcodes/isbn-numbers-for-books/