Today we had an interesting situation where an iPhone and iPad device would not connect to a new network WIFI. We were able to connect with android devices and a window laptops. No matter what settings we changed, the Apple devices would not connect.
After calling Apple and going through various suggestions including the iPad may not be compatible with the router, we found an easy fix. Invert the case sensitivity of the password. I know this makes no sense. We had a password that was lowercase and verified such with the other devices. We typed in the password on the Apple devices using UPPERCASE and they were able to join the network.
We're posting this because upon Googling this situation we saw many people having the same issue.