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I have what will be, with newest additions, an eleven volume numbered series spanning one logical collection.
I want to make it easy for readers to add all eleven volumes to their Amazon cart with minimum hassle.
Are there better options than an ordered list, on a page on my website, target to _blank, to individual volumes on my website?
Two approaches that you can take here (either or both as you prefer):
Assuming these are KDP books I'd make sure you set the collection up as a series in your KDP account. The customers can't add them all in one go but they can easily see them together and add them individually relatively easily.
Since they're your books there's nothing to prevent you creating a new "omnibus" edition with a new ISBN that contains all of the existing volumes in one. You can then sell that omnibus at a discounted rate vs buying individually etc.
