Wallet apps should start integrating "proof of payment", so the wallet sends back the pre-image to the nostr client after the payment.
Discussion
Is an invoice, in your wallet you receive the pay, is doesn’t matter who pay the invoice, you receive the sats, I don’t think is important to send back an image or recipe of the pay, you can always the person who pay can take a photo os the transaction
A pre-image is a better proof than a screenshot, still not perfect because it's not only known to the actual sender, but that would be fixed with PTLCs.
Just a better & more reliable version of the 'paid' reply.
In a situation you need to know who paid the invoice, but the invoice normally you send directly to a person don’t broadcast to everyone, normally you broadcast a lnurl because you want an “invoice” don’t close after the paid, could be a good adon but I don’t se to be a mandatory feature