API upload corrupted

Hi,

I'm a novice coder. Can someone take a look at the following method and tell me if I'm doing something wrong? Sometimes the files I upload to dropbox are corrupts. I'm working with large audiovisual files. This doesn't always happen. Only occasionally.

# Uploads file to dropbox
def upload_file_to_dropbox(self, file_path, dropbox_path, max_retries=5):
    for attempt in range(max_retries):
        try:
            #Step 0: Check if ACCESS_TOKEN is still valid
            if self.token_expired():
                self.refresh_access_token()

            # Step 1: Initiate an upload session
            session_start_url = 'https://content.dropboxapi.com/2/files/upload_session/start'
            headers = {
                'Authorization': 'Bearer ' + self.ACCESS_TOKEN,
                'Content-Type': 'application/octet-stream'
            }
            response = requests.post(session_start_url, headers=headers)
            if response.status_code != 200:
                print("Failed to initiate upload session:", response.text)
                return

            session_id = response.json()['session_id']
            offset = 0

            # Step 2: Upload the file in chunks
            chunk_size = 4 * 1024 * 1024  # 4MB chunk size
            with open(file_path, 'rb') as file:
                while True:
                    if self.token_expired():
                        self.refresh_access_token()

                    chunk = file.read(chunk_size)
                    if not chunk:
                        break
                    upload_url = 'https://content.dropboxapi.com/2/files/upload_session/append_v2'
                    headers = {
                        'Authorization': 'Bearer ' + self.ACCESS_TOKEN,
                        'Content-Type': 'application/octet-stream',
                        'Dropbox-API-Arg': '{"cursor": {"session_id": "' + session_id + '", "offset": ' + str(offset) + '}}'
                    }
                    response = requests.post(upload_url, headers=headers, data=chunk)

                    if response.status_code == 429:
                        seconds = response.json()["error"]["retry_after"]
                        for i in range(seconds, 0, -1):
                            sys.stdout.write("\rToo many requests. Retrying chunk upload in {:2d} seconds.".format(i))
                            sys.stdout.flush()
                            time.sleep(1)
                        continue
                    # eventually edit this statement for exponential back off
                    # for some reason dropbox outputs this response as HTML, instead of JSON
                    elif 'Error: 503' in response.text:
                        seconds = 10
                        for i in range(seconds, 0, -1):
                            sys.stdout.write("\rDropbox service availability issue. Retrying chunk upload in {:2d} seconds.".format(i))
                            sys.stdout.flush()
                            time.sleep(1)
                        continue
                    elif response.status_code != 200:
                        print("Failed to upload chunk:", response.text)
                        return

                    offset += len(chunk)
                    self.bytes_read += len(chunk)
                    progress = min(self.bytes_read / self.total_size, 1.0) * 100
                    sys.stdout.write(f"\rUpload progress: {progress:.2f}% ({self.bytes_read}/{self.total_size} bytes)")
                    sys.stdout.flush()

            # Step 3: Complete the upload session
            session_finish_url = 'https://content.dropboxapi.com/2/files/upload_session/finish'
            headers = {
                'Authorization': 'Bearer ' + self.ACCESS_TOKEN,
                'Content-Type': 'application/octet-stream',
                'Dropbox-API-Arg': '{"cursor": {"session_id": "' + session_id + '", "offset": ' + str(offset) + '}, "commit": {"path": "' + dropbox_path + '", "mode": "add", "autorename": true, "mute": false}}'
            }
            response = requests.post(session_finish_url, headers=headers, timeout=30)
            if response.status_code != 200:
                print("Failed to complete upload session:", response.text)
                return
            return  # Exit the function after successful upload

        except ConnectionError as e:
            if attempt < max_retries - 1:
                print(f"ConnectionError: Retry attempt {attempt + 1}")
            else:
                raise e