To set the SSID to only 2.4GHz, you can configure that under the advanced settings under your Network (step 1):

If you can connect only one device at the time, but each of your devices, could it be that all devices have the same MAC address? Normally MAC addresses are configured to be unique from the factory, but it can be overridden. It almost sounds like they have the same MAC address, and because the identifier on the network is the MAC address, you can't have multiple devices with the same MAC.
Configuration looks quite standard and should not give issues. You may try if there is newer firmware, but without active support contract you can only use the firmware check under maintenance to get to a recent stable version.
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Herman Robers
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If you have urgent issues, always contact your Aruba partner, distributor, or Aruba TAC Support. Check
https://www.arubanetworks.com/support-services/contact-support/ for how to contact Aruba TAC. Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
In case your problem is solved, please invest the time to post a follow-up with the information on how you solved it. Others can benefit from that.
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Original Message:
Sent: Jul 17, 2023 03:51 PM
From: usuee
Subject: Configuration of an AP-503H
Beating my head against the wall.
I have a few AP-503H that I am trying to run in stand alone mode. They only need to connect four Beaglebone SBC to the network, but I can't seem to get them to do that. I have two that I am trying to work on and one in a lab.
One of them only connects to the four SBCs. No matter what I do, I can only get two of them to connect at a time at most. It is not the same two either. I have gotten all four to connect, but not at the same time. I keep rebooting the SBCs trying to get a second, or third to connect and nothing happens. Turn one off, and another might connect. The SBCs only use 802.11g. I would like to turn off the 5 GHz radios, but can't seem to figure out how to do that either.
The other one, I was able to reach via network. Over the weekend, it was powered down and back up. Now, it will not ping the switch it is connected to and the switch can't ping it. I have used a laptop to get on the wireless network to access the webpage and everything seems fine but it can't ping the gateway. I have rebooted the wap and that did not help.
I opened a case with HPE TAC, but it seems I did not buy foundation care so they won't help me. My vendor missed an opportunity there.
I have attached a version of one of my configs. I am just at my wits end. I have read portions of the manual over and over again trying to get this to work. I am not trying to do anything that should be this hard.