Why might my API route be returning HTML instead of JSON in Next.js?

Several reasons could cause this: 1. **Unhandled Exceptions:** An uncaught exception in your API route could lead to Next.js rendering a default error page (which is HTML). 2. **Incorrect `res.status()` and `res.json()` Usage:** You might be setting an error status code (e.g., 500) without then sending a JSON response, causing the default error page to be returned. 3. **External API Issues:** If your API route relies on an external API, that API might be returning an HTML error page, which your route is then passing back. 4. **Middleware problems:** Incorrect configurations or errors in middleware can redirect requests unexpectedly or modify responses incorrectly.