If the app prompts you to switch to EasyPark Small, it's usually because you're using a local parking package but attempting to park in an area not managed by the City. The local package is only valid for parking spots owned by the City, so it cannot be used outside of those designated areas.
If you still wish to proceed with parking, simply confirm the switch to EasyPark Small and follow the instructions provided in the app.
If you are not able to make this change in the app you can do it via the website. By logging on to your account you have a subscription option where you can choose package.