Text-to-speech fetch request - Error 400: "Input type has to be text or SSML"

[tourai]

Hi! I'm making a React Native app and want to fetch TTS data from the following endpoint: https://texttospeech.googleapis.com/v1beta1/text:synthesize

However, when I run my code, I get the following error: {"error": {"code": 400, "message": "Input type has to be text or SSML. Maybe the input is empty?", "status": "INVALID_ARGUMENT"}}

My code is below:

const API_KEY = "...";
const API_URL = `https://texttospeech.googleapis.com/v1beta1/text:synthesize?key=${API_KEY}`;

const speak = async (text) => {
  try {
    console.log("sup");
    const response = await fetch(`${API_URL}`, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: {
        input: {
          text: "Hello world",
        },
        voice: {
          languageCode: "en-US",
          name: "en-US-Wavenet-A",
          ssmlGender: "MALE",
        },
        audioConfig: {
          audioEncoding: "MP3",
        },
      },
    });
    const result = await response.json();
    console.log(result);
  } catch (error) {
    console.error("Error:", error);
  }
};

As you can see, the input type is text. I've also tried changing the type to SSML, but with no luck (I get the same error). What can I do? Any help would be much appreciated!