Upload to AnkiWeb fails after field changes with vague network error

Anki Syncing & AnkiWeb
1

Problem Summary

After adding new fields to my Anki cards / note types, Anki detected a sync conflict between my local collection and AnkiWeb.

When the conflict dialog appears, I choose:

Upload to AnkiWeb

because I want to overwrite AnkiWeb with the collection from my desktop.

However, the upload fails with a generic network error, and the error details do not show a useful URL or diagnostic information.

Conflict Dialog Shown

Anki shows the following message:

A network error occurred.

Error details: <U+2068>error sending request for url ()<U+2069>

Environment

  • Anki version: 25.09.4
  • Platform: Windows 10 pro edu
  • Sync target: AnkiWeb
  • Sync action attempted: Upload local desktop collection to AnkiWeb
  • Trigger before issue: Added new fields to cards / note types
  • Network tools/proxies/VPN: Disabled during testing

Actions Performed

  1. Disabled all proxy/VPN/V2Ray tools.
  2. Verified HTTPS connectivity using curl -v.
  3. Confirmed successful TCP/TLS connection and 200 OK response.
  4. Tested MTU and detected packet loss with larger packets.
  5. Reduced Windows Ethernet MTU to 1300.
  6. Confirmed stable ping after MTU adjustment.
  7. Removed/disabled Outline TAP adapter to avoid routing conflicts.
  8. Reset Windows Winsock and IP stack.
  9. Checked MikroTik router configuration.
  10. Verified LTE interface MTU behavior.
  11. Temporarily disabled FastTrack.
  12. Applied MSS clamping to reduce fragmentation risk.
  13. Verified MikroTik access to Anki servers using /tool fetch.
  14. Tested multiple DNS providers.
  15. Selected stable DNS servers: 1.1.1.1 and 9.9.9.9.
  16. Checked Windows Firewall rules.
  17. Verified that Anki was not clearly blocked.
  18. Checked Windows Time service.
  19. Started/repaired W32Time.
  20. Configured NTP synchronization to reduce TLS certificate validation risks.

plzzzzzzzzzzzz help meeeeeeeeeeeee

2

It’s unlikely the syncing failure is related to you doing a one-way sync. That’s just a normal error that can happen when the app can’t reach AnkiWeb’s servers. Error establishing a secure connection when syncing - Anki FAQs

It looks like you’ve tried a lot of things already, so it might just be a passing internet connection issue. If this device, on this internet connection, was syncing successfully before – you should think about what might have changed since then, with your internet connection, with your operating system, with other 3rd-party apps on your device, etc.

3

Hi, I recently started experiencing the same error message, but in a slightly different situation. Anki Desktop appears to successfully sync/upload changes to AnkiWeb, but when I close the app and the media sync/upload process begins, it starts syncing media and then this error message pops up before the app closes.

Nothing has changed on my computer since this was working normally, so I’m not sure what triggered it. Were you ever able to resolve this?

4

  1. Have you tried any of the things I suggested above?

  2. Have you cleaned up your unused media lately? Run Check Media > Delete Unused Media

5

Hi. I appreciate your response! The issue seemed to just resolve itself. Maybe a passing internet issue as you suggested.

6

Many thanks to everyone who tried to help. I found the problem. The issue was due to the JavaScript code snippets I added, and after removing the JavaScript code, the problem was completely resolved and the decks synced.

7

I had already done that, but I forgot to mention it in the list of steps I took that didn’t work.