"Invalid JSON response: null" error when using Gemini Pro Vision AI API in Node.js

Question

I am trying to use the Gemini Pro Vision AI API in my Node.js application to generate text based on a prompt. However, I am receiving an "Invalid JSON response: null" error when I send a request to the /speech endpoint.

I have tried the following:

Verified that my API key is correct. Tested the endpoint using Postman and received a successful response. Checked the server-side code for errors in JSON serialization. I am not sure what is causing the error and would appreciate any help in debugging this issue.

async function sendPrompt(file, prompt, language) {
  try {
    const datasend = { file, prompt, language };
    const jsonData = JSON.stringify(datasend);

    const response = await fetch("/speech", {
      method: "POST",
      headers: {
        "Content-Type": "application/json"
      },
      body: jsonData
    });

    if (response.ok) {
      const contentType = response.headers.get("content-type");
      if (contentType && contentType.includes("application/json")) {
        const data = await response.json();
        const text = data.text;
        // const image = data.file;

        // Speak the text using the p5.js library
        speech.speak(text);

        // Redirect naar de pagina met de image URL
        // window.location.href = `/generate-prompt?imageUrl=${encodeURIComponent(
        //   JSON.stringify(image) + "?imageUrl=" ${encodeURIComponent(JSON.stringify(text))}
        // )}`;
        console.log("Upload response:", data);
      } else {
        console.warn("Unexpected response format. Not JSON.");
      }
    } else {
      console.error("Failed to upload photo:", response.statusText);
    }

    console.log("Upload response:", data);
  } catch (err) {
    console.log(err);
  }
}

app.post("/speech", async (req, res) => {
  const prompt = req.body.prompt;
  const file = req.body.file;
  const language = req.body.language;
  console.log(prompt, file, language);

  if (prompt) {
    const userId = await getUserIdFromSession(req.session);
    // Call the new function
    console.log("userId", userId);
    const options = {
      method: "POST",
      url: "https://gemini-pro-vision-ai1.p.rapidapi.com/",
      headers: {
        "content-type": "application/json",
        "X-RapidAPI-Key": "71956f59b5msh089630402391f02p108b9bjsna7adb689e8c4",
        "X-RapidAPI-Host": "gemini-pro-vision-ai1.p.rapidapi.com"
      },
      data: {
        contents: [
          {
            parts: [
              {
                inline_data: {
                  mime_type: "image/png",
                  data: "https://www.takeaway.com/be/foodwiki/uploads/sites/2/2017/10/doner-kebab-3-1080x960.jpg"
                }
              },
              {
                text:
                  "gedraag je als een hulp assistent voor een blind persoon" +
                  prompt +
                  "in de volgende taal" +
                  language
              }
            ]
          }
        ]
      }
    };

    try {
      const response = await axios.request(options);
      const jsonData = response.data;
      if (jsonData && jsonData.candidates && jsonData.candidates.length > 0) {
        const text = jsonData.candidates[0].content.parts[0].text;
        console.log(text); // Log de volledige respons
        await savePrompt(prompt, file, language, userId, text);

        res.json({ text, file });
      } else {
        console.error("Invalid JSON response:", jsonData);
        // Mogelijk moet hier een fallback-logica worden toegevoegd
      }
    } catch (error) {
      console.error(error);
    }
  }
});

Verified that my API key is correct. Tested the endpoint using Postman and received a successful response. Checked the server-side code for errors in JSON serialization. I am not sure what is causing the error and would appreciate any help in debugging this issue.