wi-fi connection fail even with the right password

if you ruled out everything in the article it could be the router cant handle the request or theres a corruption in the router. There may be a limit to the number of addresses the router will give, and sometimes there may be duplicates of addresses taking away from that limit.

If you have guest wi-fi enabled start by disabling it.

if you can still connect to other wi-fi networks with the iPhone then it's most def the router.

in most cases restoring the router to factory can fix this, though sometimes it's necessary to update the firmware as well. If you do this any device connected to the router may need to be reconnected if you changed password or SSID, etc.