ChestShop-authors
VKBackpack sell
Make the contents of a backpack sell in a chestshop in the last version (1.13.2)
Unfortunately VKBackPack does not provide a public API and seeing as it's a proprietary paid plugin it's impossible to shoehorn something in unless the author decides to release a separate API-jar/maven artifact.
I suggest contacting them directly about that and maybe even about opening a PR themselves to add support to their plugin as it's more in their interest than ours that ChestShop supports their paid premium resource over some other one.
There is the asnwer from vk2gpz
VKBackPack does have APIs and that’s what other developers use. For example, clip’s AutoSell can sell contents of VKBackPack because he uses these API s.
and 1 hour after
Vk just released api resource which includes stubs for development.