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 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).

Arguments:
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

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