Device connection failure

How to troubleshoot if the router can access the Internet normally but cannot connect to the smart device?

What should be done when error codes 135, 205800 occur during device pair?

The Indicator light changed from flashing to regular,but it still fails to connect?

What should I do if the device only connects to the 2.4G WiFi band and fails to connect to the 5G WiFi band?

Why only use AP mode (blink slowly) can add device successfully, but EZ mode (Blink Quickly) does not work?

When adding a Zigbee sub-device, the message "Unauthorized, unable to add" appears, and the gateway cannot find the device. What should I do?

How to troubleshoot if Wi-Fi device fails to connect successfully?

Why the device failed to connect (Bluetooth)?

What should I do when my device fails to connect to the network?

Why the device failed to connect (Zigbee)?