Gettxoutproof

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 one of the first 16
outputs is unspent 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 in manually (by blockhash).

Return the raw transaction data.

Arguments:
1. "txids"       (string) A json array of txids to filter
    [
      "txid"     (string) A transaction hash
      ,...
    ]
2. "block hash"  (string, optional) If specified, looks for txid in the block with this hash

Result:
"data"           (string) A string that is a serialized, hex-encoded data for the proof.