"meta.offline" contains empty object.

[mastadong]

I have a React/Typescript project. I have defined my offline action interface as:

interface ISaveAirBalancesOffline{
    type:CommissioningActionTypes.SAVE_AIR_BALANCES_OFFLINE;
    payload: {selectedSystem:IEquipmentSystem | null,editedAirBalances:IUnitAirBalance[]},
        meta: {
            offline: {
                effect: (dispatch:Dispatch<CommissioningAction>) => void;
            }
        }
}

I implement this interface when I create and dispatch the action from my action-creator like this:

const offlineAction: Action = ({
                type: ActionTypes.SAVE_AIR_BALANCES_OFFLINE,
                payload: {selectedSystem,editedAirBalances},
                meta: {
                    offline: {
                        effect: async (dispatch: Dispatch<Action>) => {
                            try {
                                  /* DO SOME API STUFF *.                           
                                dispatch({
                                    type: ActionTypes.SAVE_AIR_BALANCES_SUCCESS,
                                    payload: updatedSystem,
                                });
                            } catch (err) {
                                if (err instanceof Error) {
                                    dispatch({
                                        type: ActionTypes.SAVE_AIR_BALANCES_ERROR,
                                        payload: err.message,
                                    });
                                }
                            }
                        },                   
                    },
                },
            });

    console.log(`Dispatching offline action: ${JSON.stringify(offlineAction)}`);
    dispatch(offlineAction);

When I place a breakpoint on the line 'dispatch(offlineAction)', the Redux Dev Tools show that the 'effect' contains a function. After dispatching the offlineAction, I open Redux Offline's "outbox" and find the following:

"type": "save_air_balances_offline",
  "payload": {  (This contains all the correct payload data) },
  "meta": {
    "offline": {}
  }

Note that while the "type" and "payload" are correct, the contents of "meta.offline" are empty. Here is how I've implemented Redux Offline in my (React/Typescript) application:

import offlineConfig from '@redux-offline/redux-offline/lib/defaults';
import reducers from './reducers';
import persistCallback from './middleware/persistCallback';

const customConfig = {
  ...offlineConfig,
  persistCallback: persistCallback,
};

export const store = configureStore({
  reducer: reducers,
  enhancers:[offline(customConfig)]
});

Since the documentation for Redux Offline is so sparse and some examples are outdated, I'm having a hard time working out exactly how to implement the library in my application. Does anyone have a plausible explanation for what's happening or why?