gettxoutproof ["txid",...] ( blockhash )

*bitcoin-cli help 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"       (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

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