Some units can't connect to my wifi system.. Invalid certificate..

Obiwan_Pierogi

Hello.. I can't seem to get any response from Zyxel with my problem..  ..  For years I have been using a G4200 to serve my wifi guests on my campground.. I bought an N-4100 as a spare..  This year I decided to use the N-4100. I purchased the printer from ebay, as they aren't available anymore..  Anyways, about 90% of the users can connect with no problem, but a small percentage, they get a red https, with a couple of lines through it.. It won't let them connect.. Even when they type in 1.1.1.1  ...It says there is no valid certificate, and you're obviously dealing with a crooked business who wants to steal your passwords etc.   This isn't true.. I registered the N-4100 with zyxel, but never heard anything more..    Today, I reconnected my old G4200.. I hate it as there's so many letters and numbers required to authenticate, but at least it worked..  Any Ideas?   Why is it so hard for an I-phone or laptop to connect to my wifi system?  For some the logon page just pops up after joining my hotspot.. Others.. There's no way to get them to join.. And I don't understand the certificate license..

lalaland

@obiwan_pierogi,
There is a workaround in other discussion thread, it did the trick on my site. you can try it
https://businessforum.zyxel.com/discussion/1318/zyxel-n4100-gateway-problems-with-ssl-certificate-on-welcome-page-google-chrome/p2