Wi-Fi connection may fail for the following reasons:
AP device malfunction
Verify after rebooting the power of the AP device, upgrade the AP device to the latest version, or contact the AP device manufacturers.
If an incorrect password is entered when connected to security-enabled Wi-Fi type. For example, since the letter "O" might be entered
by mistake as the number "0," confirming the password is required.
Malfunction of downloaded apps
Since some apps downloaded from Google Play store used to limit access to a Wi-Fi connection often,
it is advisable to delete the apps that are not in use.
The frequencies used by Wi-Fi are 2.4Ghz and 5Ghz band. Because the 2.4Ghz frequency band is not wide enough,
and many kinds of equipment use this bandwidth in common, there can be a lot of frequency interferences.
Since the 5Ghz band has less interference, you can connect to the AP in the 5Ghz band to use the Wi-Fi with more ease.