Promise In Next Config

Why This Error Occurred

The webpack function in next.config.js returned a promise which is not supported in Next.js. For example, below is not supported:

module.exports = {
  webpack: async function (config) {
    return config
  },
}

Possible Ways to Fix It

In Next.js versions above 12.0.10, module.exports = async () => is supported.

For older versions, you can check your next.config.js for async or return Promise.

Potentially a plugin is returning a Promise from the webpack function.