EC2 with Docker and Flask API File Upload

hello everyone, i have a docker instance running on an aws ec2 instance. on the docker container i have a flask server running. Now i am trying to upload a image file via post from a local python file. But somehow the file gets corrupted during upload. i am not able to open the image with Pillow. on my local machine the file is correct. if i do the same setup with the same code and docker container on my local instance everything works.

file testFolder/input.png testFolder/input.png: PNG image data, 1024 x 1024, 8-bit/color RGB, non-interlaced but on the server its broken

file input.png input.png: data

my client code:

# client.py

import requests

url = ''
apiKey = ""
headers = {'x-api-key': apiKey}
files = {'file': open('input.png', 'rb')}

response = requests.post(url, files=files, headers=headers)

print(response.text)

my server code:

# server.py

from flask import Flask, request, jsonify
import os

app = Flask(__name__)

@app.route('/upload', methods=['POST'])
def upload_file():
    if 'file' not in request.files:
        return jsonify(message="No file part"), 400

    file = request.files['file']

    if file.filename == '':
        return jsonify(message="No selected file"), 400

    if file and file.filename.endswith('.png'):
        file_path = os.path.join('uploads', file.filename)
        file.save(file_path)
        return jsonify(message="File uploaded successfully", file_path=file_path), 200
    else:
        return jsonify(message="Invalid file format, only ZIP allowed"), 400

if __name__ == '__main__':
    if not os.path.exists('uploads'):
        os.makedirs('uploads')

    app.run(host='0.0.0.0', port=80, debug=True)

if i copy the file via scp the file is correct. the normal stuff like sending a request and reciving an answer is working correctly. only the file upload is broken somehow. is there any specific configuration to enable file upload to the ec2 instance with the running docker container. (security groups, ACLs ...) thank you