The body is String similar to [this](https://i.stack.imgur.com/dHf6c.png). I tried many different ways as below, but none worked.

```
await http.post(
  Uri.parse(url),
  headers: {
    "content-type": "application/json",
  },
  body: "3ea9554d-7a1f-4f20-f6f5-08da74d069a8",      // "'a' is invalid within a number, immediately after a sign character
  // body: "\"3ea9554d-7a1f-4f20-f6f5-08da74d069a8\"",  // The JSON value could not be converted to
  // body: jsonEncode("3ea9554d-7a1f-4f20-f6f5-08da74d069a8"), // The JSON value could not be converted to
  // body: jsonEncode("\"3ea9554d-7a1f-4f20-f6f5-08da74d069a8\""), // The JSON value could not be converted to
  // body: jsonEncode(jsonDecode('3ea9554d-7a1f-4f20-f6f5-08da74d069a8')),  // FormatException: Missing expected digit (at character 3)
  // body: jsonEncode(jsonDecode("\"3ea9554d-7a1f-4f20-f6f5-08da74d069a8\"")),  // The JSON value could not be converted to
);

```