If you dispatch an action with an undefined or invalid type in Redux Toolkit (or Redux in general), the store will ignore it because every reducer relies on a valid action.type to determine how the state should change.
If action.type is undefined, Redux will throw an error since action objects must have a string type property.
If the type doesn’t match any reducer case, the store simply returns the current state — no changes occur.
Middleware like thunks or loggers might still receive the action, but it won’t update the state unless explicitly handled.
To prevent these issues, always use auto-generated action creators from createSlice() or createAction(). These utilities guarantee correctly structured action objects with valid types.