My father in law can't connect to his Plusnet wifi on his iPhone - it was fine until a couple of days ago but now it says his password is wrong. I can connect to the wifi fine. But even when I share my password (which clearly works) automatically to his phone he still gets an "wrong password" error message and can't join the wifi network.
We've done all the iPhone reset, router reset etc.
I am very sorry that you are having problems with your father in laws Wi-Fi connection. My general advice would be to factory reset the router but pressing something small and thin into the reset hole for around 20 seconds.
If this doesn’t work please can you ask you’re farther in law to contact us so we can look into this further with them.