Iphone 8 not accepting wi-fi password

What happens if you temporarily change the name of the Wi-Fi network on your modem/router and use the same password?

Can the iPhone connect that way? If yes, the Wi-Fi settings on the iPhone for the old password were corrupted, even if you "forgot" the network on the iPhone. Keep the "new" network that you set up.

If the iPhone still can't connect using a different network name as a test.....then the puzzle continues.

The router password is not always the same as the Wi-Fi password.

To find out the correct Wi-Fi password, you must log in to the router.

The Wi-Fi network name, or SSID (service set identifier), is the name your network that has a password.

That is your Wi-Fi password.

See -> Recommended settings for Wi-Fi routers and access points

Recommended settings for Wi-Fi routers and access points - Apple Support