Using fedi-alpha on fedi network, seems to have an offline feature. Have yet to test it out.have been able to send sats to usernames via chat

Hmm i have never done that so that would be creating a psbt partially signed bitcoin transaction, then signing it and then giving that transaction to the vendor for them to broadcast the transaction when they have internet. I suppose that’s possible Because you can see the transaction info in your wallet before you broadcast it but I would imagine there is a way this can be “double spent” or otherwise cheated as its just a transaction that you can’t confirm becusee you don’t have Internet. I’m curious if this can be done securely. That being said I have seen cool implementations offline lightning ATMs and games