String Interpolated base url and end point not working on Flutter Web app

Question

I have implemented a flutter web app and created develop and release environments. I am accessing the API Url like "${ConfigEnv.baseUrl}${MyEndPointFile.jokesEndPoint}", . The Config File looks like below:

class ConfigEnv{
   static String get fileName {
    if(kReleaseMode){
      return '.env.production';
    }
    return '.env.develop';
  }

  static String get baseUrl{
    return dotenv.env['API_URL'] ?? '';
  }
}

When I run my web app locally in develop mode or release mode then the correct base urls are picked as written in .env file but when I host the web app to custom domain then the base url is getting replaced by the domain name of my hosted web app. To simplify and debug the problem, when I replace the interpolated string (baseUrl+endPoint) by complete hardcoded API URL then it is working on deployed live website as well. Why is this happening and how to resolve this?