Please check the handset settings and ensure the connected Wifi has no Proxy configured.
Android Users:
Go to Settings and click Connections, click Wi-Fi.
Your current network will be specified, please click the settings cog symbol.
Once the Wi-Fi settings open click View More scroll down and click Proxy and ensure this is set to None.
iPhone users:
Go to Settings and click Wi-Fi.
Click the I icon next to the Wi-Fi network you want to check the Proxy for.
Scroll down and click Configure Proxy and ensure this is set to off.