Verify canary release

• I verified that the issue exists in Next.js canary release

Provide environment information

Operating System:
     Platform: linux
      Arch: x64
      Version: #1 SMP Tue Jun 23 12:58:10 UTC 2020
    Binaries:
      Node: 14.17.3
      npm: 6.14.13
      Yarn: 1.22.17
      pnpm: N/A
    Relevant packages:
      next: 12.1.5
      react: 18.0.0
      react-dom: 18.0.0

What browser are you using? (if relevant)

Chrome 102.0.5005.61

How are you deploying your application? (if relevant)

Vercel

Describe the Bug

I am attempting to use res.unstable_revalidate to revalidate an ISR generated page. When invoking the function, the following error is returned ->

export default async function handler(
  req: NextApiRequest,
  res: NextApiResponse
) {
  if (req.query.secret !== process.env.ISR_REVALIDATION) {
    return res.status(401).json({ message: 'Invalid token' });
  }

  if (!req.body.path) {
    return res
      .status(400)
      .json({ message: 'Please provide a path to revalidate' });
  }

  try {
    await res.unstable_revalidate(req.body.path);
    return res.json({
      message: `${req.body.path} Revalidated`,
      revalidated: true,
    });
  } catch (err) {
    // If there was an error, Next.js will continue
    // to show the last successfully generated page
    return res.status(500).send('Error revalidating');
  }
}

TypeError: res.hasHeader is not a function

The error will not be returned if I pass just the index route, /. However, any other path that is passed in from a ISR page will return TypeError: res.hasHeader is not a function

Full stack trace

at handler (webpack-internal:///(api)/./src/pages/api/revalidate.ts:30:21)
at processTicksAndRejections (internal/process/task_queues.js:95:5)
at async Object.apiResolver (/node_modules/next/dist/server/api-utils/node.js:185:9)
at async DevServer.runApi (/node_modules/next/dist/server/next-server.js:404:9)
at async Object.fn (/node_modules/next/dist/server/base-server.js:507:37)
at async Router.execute (/node_modules/next/dist/server/router.js:212:36)
at async DevServer.run (/node_modules/next/dist/server/base-server.js:642:29)
at async DevServer.run (/node_modules/next/dist/server/dev/next-dev-server.js:514:20)
at async DevServer.handleRequest (/node_modules/next/dist/server/base-server.js:334:20)

Expected Behavior

To run the function and trigger a revalidation

To Reproduce

Trigger res.unstable_revalidate and pass whatever path you want to revalidate.