How do I upload files from a phone to my Amazon S3 server? - unity3d

Question

I'm developing a mobile app with Unity and using S3 to store and retrieve assets, I can download asset bundles just fine from the server to the phone, but how do I upload files from the phone to the server?
I used the PostObject function from the AWS Unity SDK, and it works fine if I upload from the computer as I know the directory, but I'm not sure how to get the phone's photo gallery to upload to the s3 server.
This is the PostObject function
public void PostObject(string fileName)
{
ResultText.text = "Retrieving the file";
var stream = new FileStream("file://" + Application.streamingAssetsPath + "/" + fileName,
FileMode.Open, FileAccess.Read, FileShare.Read);
Debug.Log("kek");
ResultText.text += "\nCreating request object";
var request = new PostObjectRequest()
{
Bucket = S3BucketName,
Key = fileName,
InputStream = stream,
CannedACL = S3CannedACL.Private,
Region = _S3Region
};
ResultText.text += "\nMaking HTTP post call";
Client.PostObjectAsync(request, (responseObj) =>
{
if (responseObj.Exception == null)
{
ResultText.text += string.Format("\nobject {0} posted to bucket {1}",
responseObj.Request.Key, responseObj.Request.Bucket);
}
else
{
ResultText.text += "\nException while posting the result object";
ResultText.text += string.Format("\n receieved error {0}",
responseObj.Response.HttpStatusCode.ToString());
}
});
}
And this is where I'm using it to upload the picture taken from the phone to the server
public void TakePicture(int maxSize)
{
NativeCamera.Permission permission = NativeCamera.TakePicture((path) =>
{
Debug.Log("Image path: " + path);
if (path != null)
{
// Create a Texture2D from the captured image
Texture2D imageTexture = NativeCamera.LoadImageAtPath(path, maxSize);
if (imageTexture == null)
{
Debug.Log("Couldn't load texture from " + path);
return;
}
//picturePreview.gameObject.SetActive(true);
//picturePreview.texture = imageTexture;
Texture2D readableTexture = DuplicateTexture(imageTexture);
StartCoroutine(AddImageJob(readableTexture));
//Saves taken photo to the Image Gallery
if (isSaveFiles)
{
NativeGallery.SaveImageToGallery(imageTexture, "AReview", "test");
//Upload to Amazon S3
aws.PostObject(imageTexture.name);
aws.PostObject("test");
}
}
}, maxSize);
Debug.Log("Permission result: " + permission);
}
Any clues?
Thank you.