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 (json array, required) The txids to filter
"txid", (string) A transaction hash
2. blockhash (string, optional) If specified, looks for txid in the block with this hash
"str" (string) A string that is a serialized, hex-encoded data for the proof.