1. Check your iOS Settings -> Privacy -> Reminders and make sure Paprika has permission to access your Reminders.
2. If you have iCloud set up on your device, you will also need to allow iCloud to sync Reminders under iOS Settings -> iCloud.
3. If after following the above two steps you still get this error message, try creating a list in Reminders named "Paprika" first.
(If you are exporting a custom list instead of the default list named "My Grocery List", use the name of that list instead. For example, if you have added a custom list in Paprika named "Weekly Shopping" then create a corresponding list in Reminders named "Weekly Shopping".)