There's a problem with the connection to the Blizzard servers.
Before you can connect to the game servers, you must add a phone number to this account.
Troubleshooting steps to help you connect to Hearthstone
Troubleshooting step for connection-related problems on Windows.
Troubleshooting steps for problems connecting to Hearthstone.
How to troubleshoot connection issues between Battle.net and Steam
Troubleshooting game or Battle.net services connection error BLZBNTAGT00000BB8
Troubleshooting steps to help you connect to the Battle.net desktop app.
Information on troubleshooting connection and installation issues using another network.