Uploading image with fetch (formdata), results in 400 bad file format

I have been struggling with image upload for days.
I’m using formdata like this:

      let formData = new FormData();
      formData.append('file', {
        uri: uri,
        name: `name`,
        type: `image/jpeg`,

uri on iOS is something like ''asset-library://asset/path" on Android it is like “content://media/external/images/media/25377”

      let options = {
        method: 'POST',
        body: formData,
        headers: {
          Accept: 'application/json',
          'Authorization': 'Bearer ' + token,

let response = await fetch("https://myserverurl", options)

I tried every trick reading the image as blob, removing content-type, other libraries like axios, etc…
No matter what I always get back a 400 bad file format error.

Is there something I’m missing with formdata?
(On the backend we use ASP.NET)

Did you find a solution? I am stuck on th same boat