Traffic will always be active as long as you have an internet connection, but you can choose to make it visible on the map or hide it. On the Map, tap on the the Traffic button to enable it and tap again to disable it
Make sure you have an internet connection, either mobile data or wifi, otherwise Karta GPS won't be able to get live traffic information to help you on route suggestions and estimated times of arrival.
If you still can't view traffic information, please have in mind that Karta GPS is offering 6 months of free traffic information valid from the date you installed the app for the first time. After that period, when tapping the Traffic button you’ll be redirected to the Downloads section, where you can purchase the Traffic service forever.