Just send it and double spend it if they don't receive it?
nostr:nprofile1qqs9pk20ctv9srrg9vr354p03v0rrgsqkpggh2u45va77zz4mu5p6ccpzemhxue69uhk2er9dchxummnw3ezumrpdejz7qgkwaehxw309a5xjum59ehx7um5wghxcctwvshszrnhwden5te0dehhxtnvdakz7qrxnfk I wonder if an e-cash token can be officially expiring so that if someone tries to claim it later on, they understand why they can't. While the sender has the "master key" to recover the funds.
Discussion
Well it's the difference between the receiver seeing an error that states: "the offer expired", vs "the token was spent".