Error E03 indicates that although the Smart AC Control is connected to Wi-Fi, the router did not transmit an IP address to the device. To allow the Smart AC Control to obtain an IP address, enable DHCP in the router settings. How this is done specifically for your router can be found in your router manual.
Tip: You can always control the AC using the user interface on the Smart AC Control even when the Internet is temporarily unavailable. Your old remote control will also work in this case.