Unable to communicate with Express API after building to PROD

[Divine Nomana Azianka]

I'm building a nuxtjs project which requires Express JS as server-side. I'm using the serverMiddleware property to connect to the index.js.
This method works well in dev mood. I'm able to communicate with the API's. But after building (bundling) the project, it changes the url to "app://./" instead of "localhost:{port}/". And this prevents the API from working.