PUT Requests storing empty JSON object

I am trying to update text files on my pod using a PUT request. If I have a text file, e.g. /public/hello.txt and make a PUT request to override its value, the file is replaced by a text file with an empty JSON object.

Here's a snipped of the code I used to perform the PUT request. Here we are assuming /public/hello.txt exists already.

url = "https://boulderwebdev.solid.community/public/hello.txt"
solid.fetch(url, {
  method: "PUT",
  headers: {
    "Content-Type": "text/plain"
  },
  body: JSON.stringify({"hello": "world"})
}).then(resp => {...})

If you go to https://boulderwebdev.solid.community/public/hello.txt now you will see a page with the text

{}