gettxoutproof ["txid",...] ( blockhash )
Returns a hex-encoded proof that "txid" was included in a block.
NOTE: By default this function only works sometimes. This is when there is an
unspent output in the utxo for this transaction. To make it always work,
you need to maintain a transaction index, using the -txindex command line option or
specify the block in which the transaction is included manually (by blockhash).
1. "txids" (string) A json array of txids to filter
"txid" (string) A transaction hash
2. "blockhash" (string, optional) If specified, looks for txid in the block with this hash
"data" (string) A string that is a serialized, hex-encoded data for the proof.