WiFi
The latest Raspbian Buster OS requires explicit definition of the Wi-Fi Country in the Wi-Fi configuration file /etc/wpa_supplicant/wpa_supplicant.conf for Raspberry Pi 3B+ model. To set the country in that file you can either edit it manually (if you know the country code) or run raspi-config utility:
sudo raspi-config
then follow the screens (select your own country in the last screen):
The selected country will be added to the configuration file /etc/wpa_supplicant/wpa_supplicant.conf, for example:
country=US
Reboot Raspberry Pi after completing these steps:
sudo reboot
Now you can configure your Wi-Fi network using Peppy player UI.