Finally designing payer proofs, thanks for prompt nostr:nprofile1qqsr6tj32zrfn7v0pu4aheaytdnnc6rluepq73ndc2tdjzus34gat9qpz4mhxue69uhhyetvv9ujuerpd46hxtnfduhswulwwv! This proves that the invoice was requested by you, and paid, in a nice standard format. Fields which aren't needed are omitted, but you can still verify the signature. 

Was a design aim for BOLT12, but now time to bring it into the world...