message: json service use base64 private key
diff: @@ -202,7 +202,7 @@ test("sign_transaction", async () => {
  const response = await callMethod(
  URL,
  "sign_transaction",
  - [EXAMPLE_TRANSACTION, child.privateKey.toString("hex")],
  + [EXAMPLE_TRANSACTION, child.privateKey.toString("base64")],
  1,
  );
  