This is how Proof of Bitcoin Node (or any cross chain Node) needs to work, using the OP_RETURN updates in BIP74



The internal communications within the Spreadwallet make this whole thing work. The internal communications within the Spreadwallet can be similar to the way exchanges deal with transactions, they have their own ledgers that keep track of whats going on, and only when customers put money in or take money out do they interact with specific coin daemons.

Because of Bitcoin confirmation wait times, the completion of the proof might take 10 minutes or 10 days, but the relay communications can be ring fenced / locked by the servicenode network to avoid an attacker stealing payments.

If you have the required public and private keys, only you can create and confirm the hash as proof of the broadcast message.