Good morning Corne,
My understanding, it would be possible to remove proof-of-payment selectively
by hiding the payment in fees.
Basically, to anonymously donate money to a node without leaving proof of who
you are, you simply route from yourself to the payee node, then back to
yourself. You pay yourself the minimum HTLC forwarding amount, and leave a
hefty fee to the payee node.
The payee cannot prove that you paid to it; as far as it is concerned it was
just a payment forwarding.
The payer cannot prove that it paid the payee, since anyone on the route other
than the payee could have been the source of the payment. This assumes that
the payer does not control the entire route, at least.
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