Need help with defining onSuccess callback for useSWR

[sfdcale]

I posted this question here(vercel/swr#362) 2 days ago but didn't receive any response, hence posting here.

I am trying to use onSuccess callback function on useSWR with no success, here is the simplified but reproducible code:

useSWR("/api/data", fetcher, { onSuccess: 
    (data, key, config) => {
      console.log('Entered onSuccess'); 
      console.log({data}); //This always prints undefined.
    }
  }
);

/api/data.js:

export default (req, res) => {
    res.statusCode = 200;
    res.setHeader('Content-Type', 'application/json');
    res.send({ FirstName: "John", LastName: "Doe"});
}

package.json:

"next": "^9.0.6",
"swr": "^0.2.0"

Here is the codesandbox showing the problem : https://codesandbox.io/s/nervous-hill-mn0kz?file=/pages/index.js

[timneutkens]

Was answered here: vercel/swr#362