Mug Life may not function if your device is unable to reach the Internet.
The most common source of network problems is a firewall blocking communication.
When using public Wi-fi, you may need to go to your internet browser and agree to a web page before it will allow you to access the Internet. Some office firewalls interfere with secure communication, which can cause problems for Mug Life.
On phones, try disabling Wi-fi to see if Mug Life will work over a cellular connection. If that fixes the problem, you know that the Wi-fi network's firewall was blocking communication. In that case, you can keep using cellular, find a different Wi-fi network, use a VPN to bypass the firewall, or figure out how to solve the problem on the Wi-fi network.
If your device's clock is set wrong, that can sometimes cause communication problems.
Under both Android and iOS Settings: General -> Date & Time -> enable Set Automatically. If that was disabled, you may need to terminate and restart Mug Life.
In some cases, terminating and restarting Mug Life may resolve a network problem. You can see how to terminate an app here: