Allow producing "payment proofs" for offline transactions too #1975
Description
Current situation
As of today (v7.5) Payment proofs can only be produced for online transactions.
Solution we would like
From the user's point of view, the need of having a payment proof is independent of the type of transaction (online / offline) that was used. It would thus make natural sense to be able to produce such proofs for both online and offline transactions.
Remarks
Ask explained by @valdok, such a proof for an offline transaction is possible. But it's a different kind of a proof than the ones for online transactions. Nonetheless, he confirms that the possibility of such a proof was indeed designed into the protocol.