Send binary data as file to API using Expo - react-native

Question

I would like to know if there is any way to send binary data that is not an image or a video in Expo to an API expecting a file as part of the FormData received.
The API expects binary data so I cannot allow myself to convert it to base64 like people advice to do.
This is what I use today, the server does not recognize a file field.
const form = new FormData();
form.append('url', downloadurl);
form.append('pageUrl', payload.link);
form.append('name', payload.name);
form.append('file', new Blob([buffer]), 'file');
const res = await fetch(endpoint, {
method: 'POST',
headers: {
'Content-Type': 'multipart/form-data',
},
body: form,
});
EDIT
The following snippet seems to send the blob to the backend. However, the blob size is nearly double the size of the array, which results in the file being received corrupted.
const blob = new Blob([buffer.raw], {
type: 'application/octet-stream',
});
// Here it logs blob with 47000 size, 25330, 25330
console.log(blob, buffer.raw.length, buffer.raw.byteLength);
const url = URL.createObjectURL(blob);
const file = {
uri: url,
type: 'application/octet-stream',
name: 'torrent',
};
const formData = new FormData();
formData.append('torrent', file as any);
formData.append('url', downloadurl);
formData.append('pageUrl', payload.link);
formData.append('name', payload.name);
const xhr = new XMLHttpRequest();
xhr.open('POST', endpoint);
xhr.onload = () => {
console.log('DONE', xhr.status);
};
xhr.send(formData);