Upload images via the developer API with node.js

I'm trying to upload images to my website through the commerce API with node.js.

Here is my code so far. FormData and fetch have been imported. 

const form = new FormData();
    form.append("file", fs.readFileSync("image.png"));
    const send_img = await fetch(
      "https://api.squarespace.com/1.0/commerce/products/" + image_id + "/images",
      {
        method: "POST",
        headers: {
          Authorization: "Bearer " + process.env.SQUARESPACE_API_KEY,
          "User-Agent": "MY-USER-AGENT",
          "Content-Type": "multipart/form-data",
        },
        body: form,
      }
    );

I keep getting this error. 

{
  type: 'INVALID_REQUEST_ERROR',
  subtype: null,
  message: "Expected exactly one file part named 'file', but found none.",
  details: null,
  contextId: 'EPOYCREESOOSLEEWRAWX'
}

Can someone help me resolve this error ?