I cannot login to the forum using my iPhone 7, iOS 11.2.6. I get an error message that the password or ID is invalid.

The password and ID is the same that I use to login on my desktop, with no problems.

 

Are you working with Safari or Chrome? do you have pop ups blocked? I'd start by clearing your browser cache and then rekeying both the user name and password. Also see if it behaves differently when you go into full site mode. (sorry can't test as I have an Android phone with Chrome that works fine in mobile view)

 

Clearing the cache worked this time! Thank you. I'd tried clearing it before with no success.