docs: private void signMultisigInput(Transaction tx, Transaction.SigHash hashType,
                                     boolean anyoneCanPay, @Nullable KeyParameter userKey) {
          TransactionSignature signature = tx.calculateSignature(0, serverKey, userKey, getContractScript(), hashType, anyoneCanPay);
          byte[] mySig = signature.encodeToBitcoin();
          Script scriptSig = ScriptBuilder.createMultiSigInputScriptBytes(ImmutableList.of(bestValueSignature, mySig));
          tx.getInput(0).setScriptSig(scriptSig);
      }