Error: write after end in API route

Workarounds

1. 96% success Add return after res.json()/res.send(): return res.json({ ok: true })

   return prevents execution of code below that would send another response

2. 90% success Use response.json() instead of manual write in App Router

   // App Router (app/api/route.ts):
   export async function POST(request: Request) {
     const body = await request.json();
     return Response.json({ success: true, data: body });
   }
   // Avoid res.write() / res.end() — use the Response API instead

   Sources: https://nextjs.org/docs/app/building-your-application/routing/route-handlers

3. 88% success Ensure the response body is not written to after the response has ended

   // Pages Router — add return after each response:
   export default function handler(req, res) {
     if (!req.body.name) {
       return res.status(400).json({ error: 'Name required' });
       // return prevents further writes
     }
     return res.status(200).json({ ok: true });
   }

   Sources: https://nextjs.org/docs/pages/building-your-application/routing/api-routes