Firstly, make sure you are on the 2.4GHz band.
Secondly, check whether the Wi-Fi name and password are correct.
Thirdly, check if there are any Internet connection problems. If the Wi-Fi signal is too weak, you could reset your wireless router and try again.
Fourthly, if none of the above is working, please reset your smart bub and connect to the network again. Switch the light on and off more than five times manually, and you shall see the light color turn to cool white. The cool white light shall flash twice, and then the color changes to warm white. This is your signal that the smart bulb has been reset successfully.