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Unexpected token '<', "<!DOCTYPE "... is not valid JSON

Exact error

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

What it means

Your code called response.json(), but the server returned an HTML page (often a 404 page or index.html) instead of JSON.

Likely causes

• Wrong API URL or path, so the host serves an HTML 404 or the SPA fallback.
• The API route doesn't exist in production (e.g. a static host with no backend).
• Server error page returned as HTML.

How to fix it

1. Check the Network tab: open the request and see its URL, status and HTML response.

2. Check response.ok before parsing:

   const res = await fetch(url);
   if (!res.ok) throw new Error(`${res.status}: ${await res.text()}`);
   const data = await res.json();

3. Fix the URL / base URL env var, and make sure an SPA rewrite isn't catching your /api routes.

Related errors

• 404: NOT_FOUND on Vercel
• Lovable app shows a blank white page after deploying elsewhere