Uploading to Cloudinary API - Invalid file parameter

I am working on integrating Cloudinary with my React Native app and am running into a problem when I go to upload using the Cloudinary API. I'm using React Native Image Picker to select an image from the camera roll and using that I get a source uri - example below.

I am getting an error response back from Cloudinary and I'm not sure what it's referring to. "Invalid file parameter. Make sure your file parameter does not include '[]'"

When I use the debugger, I can console log out all the params I am sending in the body of my request. Any suggestions would be much appreciated!

source.uri: /Users/IRL/Library/Developer/CoreSimulator/Devices/817C678B-7028-4C1C-95FF-E6445FDB2474/data/Containers/Data/Application/BF57AD7E-CA2A-460F-8BBD-2DA6846F5136/Documents/A2F21A21-D08C-4D60-B005-67E65A966E62.jpg

async postToCloudinary(source) {
let timestamp = (Date.now() / 1000 | 0).toString();
let api_key = ENV.cloudinary.api;
let api_secret = ENV.cloudinary.api_secret
let cloud = ENV.cloudinary.cloud_name;
let hash_string = 'timestamp=' + timestamp + api_secret
let signature = CryptoJS.SHA1(hash_string).toString();
let upload_url = 'https://api.cloudinary.com/v1_1/' + cloud + '/image/upload'

try {
  let response = await fetch(upload_url, {
    method: 'POST',
    headers: {
      'Accept': 'application/json',
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      file: {
        uri: source.uri,
        type: 'image/jpeg'
      },
      api_key: api_key,
      timestamp: timestamp,
      signature: signature
    })
  });

  let res = await response.json();
  console.log(res);
} catch(error) {
  console.log("Error: ", error);
}

}

UPDATE So I now have base64 encoding working, I think, but I am still getting the same error.

var wordArray = CryptoJS.enc.Utf8.parse(source.uri);
var file = CryptoJS.enc.Base64.stringify(wordArray);

try {
  let response = await fetch(upload_url, {
    method: 'POST',
    headers: {
      'Accept': 'application/json',
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      file: {
        uri: file,
        type: 'image/jpeg;base64'
      },
      api_key: api_key,
      timestamp: timestamp,
      signature: signature
    })
  });

So it turns out the source data I was passing in was not formatted correctly. I was able to pass it in from the ImagePicker plugin I was using as an already formatted data URI (the ImagePicker example comes with two ways to capture your source file and I was using the wrong one). I was able to get rid of the CryptoJS stuff and simply pass in file: source.uri