对于任何人寻找一个解决方案，这里是我更新的完整代码

router.post("/", async (req, res) => {
    var imageUrl = req.body.image;

    const imageBuffer = await axios.get(imageUrl, { responseType: 'arraybuffer' })
        .then((response) => {
            const buffer = new Buffer.from(response.data)
            buffer.name = 'image.png'
            return buffer
        })
        .catch((error) => {
            console.error('An error occurred while downloading the file:', error);
        });

    let jImage = await Jimp.read(imageBuffer);

    if (!jImage.hasAlpha()) { //Check if image has opacity
        jImage = jImage.opacity(1); //Add if it doesn't 
    }

    // Optional

    const w = jImage.bitmap.width;
    const h = jImage.bitmap.height;

    if ((w / h) != 1) {
        throw new functions.https.
            HttpsError("invalid-argument",
                "Image must be a square. Current ratio = " + (w / h));
    }

    const jsize = (await jImage.getBufferAsync(Jimp.AUTO)).byteLength;

    if (jsize >= 4000000) { //Check size
        throw new functions.https.
            HttpsError("invalid-argument",
                "Image must be less than 4MG currenty image is " +
                jsize + " bytes with Alpha");
    }

    await jImage.writeAsync("./image.png"); //Make PNG and wait for the file to be written

    try {
        const response = await openai.createImageVariation(
            fs.createReadStream("./image.png"),
            1,
            "256x256"
        );
        const image_url = response.data.data[0].url;
        console.log('variation :', image_url);
        res.json({ result: image_url });
    } catch (error) {
        console.error(error);
        res.status(500).json({ error: error });
    }

});