Failed to establish a new connection

I have been uploading files using the API regularly but suddenly i got a bunch of exceptions, which basically said the new connection can't be established and the network is unreachable.

Traceback (most recent call last):
File "run_ops_dashboard.py", line 11, in <module>
import dropbox_api
File "/home/natalie/python3/internal-dashboards/dropbox_api.py", line 7, in <module>
logging.info("Dropbox account info: {0}".format(client.users_get_current_account()))
File "/home/natalie/python3/internal-dashboards/venv/lib/python3.6/site-packages/dropbox/base.py", line 3277, in users_get_current_account
None,
File "/home/natalie/python3/internal-dashboards/venv/lib/python3.6/site-packages/dropbox/dropbox.py", line 234, in request
timeout=timeout)
File "/home/natalie/python3/internal-dashboards/venv/lib/python3.6/site-packages/dropbox/dropbox.py", line 325, in request_json_string_with_retry
timeout=timeout)
File "/home/natalie/python3/internal-dashboards/venv/lib/python3.6/site-packages/dropbox/dropbox.py", line 409, in request_json_string
timeout=timeout,
File "/home/natalie/python3/internal-dashboards/venv/lib/python3.6/site-packages/requests/sessions.py", line 555, in post
return self.request('POST', url, data=data, json=json, **kwargs)
File "/home/natalie/python3/internal-dashboards/venv/lib/python3.6/site-packages/requests/sessions.py", line 508, in request
resp = self.send(prep, **send_kwargs)
File "/home/natalie/python3/internal-dashboards/venv/lib/python3.6/site-packages/requests/sessions.py", line 618, in send
r = adapter.send(request, **kwargs)
File "/home/natalie/python3/internal-dashboards/venv/lib/python3.6/site-packages/requests/adapters.py", line 508, in send
raise ConnectionError(e, request=request)
requests.exceptions.ConnectionError: HTTPSConnectionPool(host='api.dropboxapi.com', port=443): Max retries exceeded with url: /2/users/get_current_account (Caused by NewConnectionError('<urllib3.connection.VerifiedHTTPSConnection object at 0x7fd3174da240>: Failed to establish a new connection: [Errno 101] Network is unreachable',))