v0 chat can't send messages after adding a custom MCP — `/chat/api/chat/blob` returns 400

v0
1

Hi,

After adding a custom MCP server to my v0 chat, sending any message fails with:

Unable to process request. Please edit your message and try again.

The MCP connects fine at session start (I see it initialize), but every send after that fails. The prompt reverts to a previous one on retry, no other feedback in the UI.

Chat ID: pyyIUGXf8ue

Setup (working before adding the MCP)

  • The chat is linked to a Vercel project that I deployed and connected manually.
  • The deploy is live and the project connection is correct on my side.
  • Sending messages worked normally before I added the custom MCP server.
  • I have not changed my default team, deleted any project, or touched the GitHub link.

So the project connection isn’t something I need recreated — I need the send flow to work again.

What DevTools shows on every send attempt

  • POST https://v0.app/chat/api/chat/blob → 400 Bad Request (repeats on each retry)
  • GET https://v0.app/api/git/status?chatId=pyyIUGXf8ue → 404 Not Found

Response body of status:

{
  "ok": false,
  "error": {
    "error": "Project link not found",
    "statusCode": 404,
    "errorCode": "10"
  }
}

This 404 is strange because the project IS connected from my side — I can see the deploy, the link in the chat sidebar, etc. It looks like v0’s internal state is out of sync with what’s actually configured, and the /chat/blob endpoint is rejecting the request because of that stale 404 on git/status.

Console also shows a Minified React error #418 and CSP violations on _vercel/speed-insights/vitals, but I’m assuming those are downstream noise once the chat is in the broken state.

What I’m asking

Not a project reset — the project connection on my side is correct. What I need is for v0 to recognize the existing link again so I can send messages. Looks like a backend state-sync issue triggered by adding the MCP.

Has anyone else hit this after adding a custom MCP? Any way to force v0 to re-read the project link without losing chat history?

Thanks!