unable to use custom configuration for effect for the plugin redux-offline

[Gizmo]

I am making use of the redux-offline plugin for offline first react-redux app. It works fine but I am facing issues with configuration.

I tried the code:

offline(...offlineConfig, {
       effect: (effect, action) => {
         console.log("Executing effect");
       }
}

The control comes to the above code after executing the code below(as expected):

meta: {
   offline: {
      effect: { url: 'xyz',method: 'POST', body:content },
      commit: {..},
      rollback: {...}
   }
}

It then throws an error: Cannot read property 'then' of undefined at line:

return config.effect(metadata.effect, action).then(function (result) {
 

The code works fine if i remove the configuration for effect. Any help?