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

Why this happens

• The request URL is wrong, so the server or a SPA fallback route returned its HTML 404 or index.html page
• Authentication expired, and the gateway redirected to an HTML login page
• A proxy, WAF, or load balancer returned its own HTML error page (502, 503, a bot challenge) instead of passing the request to the API
• The `Accept` header is missing, so the server content-negotiated its way to HTML

How to fix it

1. Log `response.status` and the first few hundred characters of the raw body before parsing, so the failure shows the real page
2. Assert on the status code and `content-type` header before calling `.json()`
3. Check the base URL and path in the failing environment. A missing `/api` prefix is the classic cause
4. Send `Accept: application/json` explicitly

Example

              const res = await request.get('/api/orders', {
  headers: { Accept: 'application/json' },
});

expect(res.status()).toBe(200);
expect(res.headers()['content-type']).toContain('application/json');
const body = await res.json();