Having issues uploading images using pre-signed POST URLs

I’m trying to upload an image using a pre-signed POST URL but it fails somewhat randomly.

Sometimes it returns the correct 204 code, but in roughly 50% of cases it returns 400 with a message:

<?xml version="1.0" encoding="UTF-8"?><Error><Code>InvalidArgument</Code><Message>Malformed JSON</Message><BucketName>XXXXXX</BucketName><RequestId>tx00000f65f55d800802749-00658c2492-d1de9a73-fra1b</RequestId><HostId>d1de9a73-fra1b-fra1-zg02</HostId></Error>

I’ve tried different boto3 and requests package versions but to no avail.

The issue started to appear on 24th December and is still occurring.

Here is the test code:

import requests

import requests
from botocore.exceptions import ClientError
import boto3


AWS_S3_ENDPOINT_URL = f"https://fra1.digitaloceanspaces.com"
do_spaces_client = boto3.client(
    "s3",
    aws_access_key_id="XXXXXXXXXXX",
    aws_secret_access_key="XXXXXXX",
    region_name="fra1",
    endpoint_url=AWS_S3_ENDPOINT_URL,
)

def create_presigned_post(
    bucket_name, key, fields=None, conditions=None, expiration=10 * 60
):
    try:
        response = do_spaces_client.generate_presigned_post(
            bucket_name,
            key,
            Fields=fields,
            Conditions=conditions,
            ExpiresIn=expiration,
        )
    except ClientError as e:
        print(e)
        return None

    return response

def upload_image_to_s3(
    s3_obj_name: str,
    img_bytes: bytes,
    presigned_url: str,
    presigned_fields,
    timeout: int = 180,
) -> int:
    files = {"file": (s3_obj_name, img_bytes)}

    resp = requests.post(
        presigned_url,
        data=presigned_fields,
        files=files,
        timeout=timeout,

    )
    print(resp.text)
    resp.raise_for_status()

    return resp.status_code

resp = create_presigned_post(bucket_name="XXXXX", 
                             key="test_image.jpg",
                fields={"Content-Type": f"image/jpeg"},
                conditions=[{"Content-Type": f"image/jpeg"}],
                             )
upload_image_to_s3(s3_obj_name="test_image_8.jpg", img_bytes=b"fejifejfejofe", 
                   presigned_url=resp['url'], presigned_fields=resp['fields'])