1. Physical environment: First, check if the SIM card is inserted into the correct slot and if all cellular antennas are installed. 
2. APN settings: Ensure that the configuration information of the APN is consistent with the one provided by the operator. 
3. Check device connectivity: Log in to the local interface of the device, use the system's built-in ICMP tool, ping 8.8.8.8 to test if it is connected. If it is, check the connectivity between your device (such as a computer or phone) and the router. 
4. Check if the SIM card is functioning properly: Remove the SIM card and install it in the phone to see if it can connect to the internet normally. 
5. Restart: Try turning off the router, wait for a few seconds, then reconnect the power and retry the network connection. 
6. Factory reset: Restore the router to factory and try again.