The viewkey is only available to the sender. It's the receiver that wants the "proof".
No it's not.
In a Monero transaction, the viewkey is only available to the sender, not the receiver.
There is a view key for every wallet for all transactions.
https://getmonero.org/knowledge-base/moneropedia/viewkeyDon't quote me and change my post.
And it's not Monero's fault that those AB users don't know how to use it. There are tons of MONERO blockchain explorers so either that guys an idiot or a lier either way he's not worth my time. Probably a dashfag trying to fud XMR on AB.