Failed to submit follow-up: HTTP error! status: 400

Support Bug Reports
1

Where does the bug appear (feature/product)?

Background Agent (GitHub, Slack, Web, Linear)

Describe the Bug

Sending a follow-up message to the Background Agent in the browser fails with the error: “Failed to submit follow-up: HTTP error! status: 400”.

Steps to Reproduce

  1. Open my active agent session in the Cursor web interface.

  2. Type a follow-up message in the chat input.

  3. Click send.

Expected Behavior

The message sends successfully and the agent processes the request.

Screenshots / Screen Recordings

2026-04-25_11-25.png
2026-04-25_11-25.png1906×960 216 KB

Operating System

Linux

Version Information

Cursor.com > Agents

For AI issues: which model did you use?

Opus 4.7 High

For AI issues: add Request ID with privacy disabled

bc-2ab9a790-de90-460d-8b25-54e6c974bfea

Additional Information

The chat / sessions worked perfectly fine until now. I want to continue the session but keep hitting this error.

Does this stop you from using Cursor

Yes - Cursor is unusable

5

Hey, this isn’t a bug on our side. You’ve hit your Pro plan usage limit, and the overage charge was declined by your card (Your card does not support this type of purchase). That’s why follow-ups return 400.

Account and billing requests are handled by our team at [email protected]. They can look into your specific situation and help you update your payment method so you can keep the session going.

6

Thank you, i just paid the last invoice. It would be better if the error told me there was a billing issue, rather than a generic HTTP error.

7

Agreed, a generic HTTP 400 doesn’t help at all here. It doesn’t make it clear this is a billing issue. I’ll pass the feedback to the team, we definitely need a clear message about the limit being exceeded or a payment problem.

Glad the invoice went through. If follow-ups still don’t start right after payment, let me know and we’ll take a look.

8

I am getting this error and it is not because of billing issues. I am on Pro Plan, paid in full till 5/21 and only at 31% useage. Why am I getting this error?
It was working 5 minutes ago and just started getting it while working.

9

This error is happening on your website (https://cursor.com/agents) not in the desktop application.
The desktop application is able to complete my coding prompts, just not your website.

10

@Stephen_Hunter, to figure out what’s returning the 400 in your case, please send:

  • The agent URL (like https://cursor.com/agents/bc-...) or just the bcId
  • The email on the account
  • The approximate time (UTC) when you first saw the error
  • Your browser and version
  • If you can, a DevTools screenshot (Network tab, the failed request to AddAsyncFollowupBackgroundComposer, and the Console)

Our error message is generic and can cover a few different causes, so without the bcId we can’t tell why it’s failing for you. The desktop agent and the web agent run on different runners, so the fact that it works in the IDE doesn’t rule anything out.