Dual band router. Customers iphone and ipad, both can not log onto 2.4. Say wrong password when attempting to join. Both can log onto 5g. Copy pasted all settings making sure both match in router. My phone can log onto both from the start.
Reset network settings on both apple pieces. No go. Create new SSID on 2.4 and keep same password and both now can log onto 2.4. Thoughts from someone with more knowledge.

Do you have symbols in the password?

Does he log onto another network with the same SSID but different password?

Is it an Arris, from ATT? My iPhone sometimes can't log in and it shows that the password entered is incorrect, even though I know it well (from the need to re-enter it so damn often). I had set up a guest network with a different SSID and password, but disabled it a long time ago. Most of the time, I can connect if I use the password for the guest network. ATT is no help at all, they don't offer a stand-alone modem for U-Verse, so I just live with it.

What router? Are the SSIDs different or the same for 2.4 and 5? If different, what's the difference between the original and the new one you created that does work (and why isn't that good enough)? If the same, how are you specifying which band to connect to?

Also, are you trying to force 40mhz on 2.4 or something? Is encryption the same on both? Can you connect if you remove the password altogether?

Provider Arris 1682. No symbols except -5G on 5G band. Do not know about another network with same ssid. Do not recall the 40mhz setting. Only difference with new ssid is added -2.4 on end of it.

I have discovered that my iPhone would not connect to my home network when I would arrive back home. I had to select it and enter the password each time.

Even after switching my SSID to the same name on 2.4 and 5. Then back to being separate. My iPhone still had connection problems. Both my Mac and iPad would stay connected, there again they never left the house.

I even signed out of Apple ID on everything and what not. Went weeks doing this and kept on denying it was the router as everything else worked.

Finally I rebooted the router for a few minutes and it's been working for over a month since then. I guess when changing the SSIDs that it did not do a full reboot or something.

KOT

Does that mean you told the device to "forget this network" ?

I've seen where Apple doesn't like when you change wifi brands/models and reuse the same SSID without telling it to forget this network, and start log in from scratch.

Had a low tech customer - helped change his Comcast Gateway password - he kept the same SSID.

I usually the SSID on those-for some reason on this job I just didn't.

Start getting calls that the Wi-Fi keeps dropping in and out and not working well at all.

I drive back out there, and as I'm talking to him in the kitchen, I glance over at the counter and see a wireless Linksys piece. He tells me, oh that's my repeater.

Doh. Repeater with same SSID but different password. Dude you could've told me..

Whicj provider- U-Verse or cable broadband? It matters.

The 40MHz setting would be made intentionally- out of the box, it comes set to 20MHz.

Sadly, not uncommon. My first questions "did you add or change anything"?

I first selected forget this network. Still no connection so I reset network settings in the general settings.

Band steering? Forcing all devices to 5Ghz... Check out those settings.