A customer service agent may ask you to flush your DNS cache and/or perform a winsock reset. That can resolve certain connection-related issues, like not being able to resolve a store URL. To do so:
- Close the MTG Arena client
- Open a Windows command prompt (cmd.exe) as an administrator
- Type ipconfig /flushdns and press enter
- Type ipconfig /registerdns and press enter
- Type ipconfig /release and press enter
- Type ipconfig /renew and press enter
- Type netsh winsock reset and press enter
- Restart your computer and launch the MTG Arena client