I get this error in my upload function using next14:

 ⨯ TypeError: res.setHeader is not a function
    at POST (webpack-internal:///(rsc)/./src/app/api/upload/route.ts:44:9)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async /Users/utdev/code/what_zip/node_modules/.pnpm/next@14.0.1_react-dom@18.2.0_react@18.2.0/node_modules/next/dist/compiled/next-server/app-route.runtime.dev.js:6:61856

This is the api route method:

export async function POST(
    req: NextApiRequest,
    res: NextApiResponse
) {
    const chunks = [];
    for await (const chunk of req.body) {
        chunks.push(chunk);
    }
    const body = Buffer.concat(chunks).toString();
    console.log("body", body);
    const { filename, fileHash, contentType } = JSON.parse(body);
    console.log({ filename, fileHash, contentType })
    const signedUrl = await getSignedUrl(
        R2,
        new PutObjectCommand({
            Bucket: R2_BUCKET_NAME,
            Key: `resources/${fileHash}/${filename}`,
            ContentType: contentType as string,
        }),
        { expiresIn: 3600 }
    );
    console.log("signedUrl", signedUrl);
    res.setHeader("Access-Control-Allow-Origin", "*");
    res.json({
        url: signedUrl,
        method: "PUT",
    });
    res.end();
}

What is wrong with setHeader?